MICRO 302 Midterm

Compare and contrast plate counts, Petroff-Hauser chamber, and turbidity measures in terms of usefulness and cautions you need to take in interpreting the data from each. Which measure live and dead cells? Which can be done quickly vs which take overnight to obtain your data? Which can work in dilute solutions (less than a million CFU/mL)? Which cannot?

(1) *Petroff-Hauser Chamber*: chamber with squares etched on a slide for liquid samples, then look at through a microscope • quick and easy • counts dead cells, small cells, clumped cells are more problematic, only work with 10^6 cells or more per mL if they are motile, it is very hard to count them (2) *turbidity*: cloudiness of a solution • the more cloudiness, the more cells • counts both living and dead cells • takes overnight to obtain data • can work with dilute solutions (3) *plate counts*: solution with known dilution is spread onto agar plates and then incubated • measures live CFU/mL • only some bacteria can be grown on nutrient agar • takes time to obtain countable colonies • need proper dilution to obtain countable colonies

why do cells need carbon, nitrogen, phosphorus, sulfur, and oxygen? what cellular components contain each of these elements?

(1) *carbon*: typical bacterial cell is 50% carbon; heterotrophs use organic carbon, autotrophs use carbon dioxide (2) *nitrogen*: exists in proteins and nucleic acids (3) *phosphorus*: required for nucleic acids and phospholipids (4) *sulfur*: present in amino acids (cysteine and methionine) and vitamins (5): *oxygen*: used in all macromolecules bulk of nitrogen in nature is ammonia, nitrogen gas, or nitrate (used in nitrogen fixation) all of these macronutrients make up over 90% of the dry weight of a bacterial cell

describe what is happening in each phase of the growth curve of bacteria in batch culture. where are persister cells typically detected?

(1) *lag phase (1st)*: synthesis of components, starting to make ribosomes and things they need (2) *exponential (log) phase (2nd)*: healthiest cells, maximum growth rate, where we calculate the growth rate of cells, reproducing as fast as they can (3) *stationary phase (3rd)*: batch culture, run out of food, more waste, dying at the same rate of reproduction, cryptic growth (4) *death phase (4th)*: dying faster than they are reproducing, persister cells are detected here

predict the phenotype of a bactoprenol-deficient mutant Staphylococcus, a gain of functional mutation of autolysin genes in E. coli, and treatment of streptococci in an isotonic solution with penicillin.

(1) a bactoprenol-deficient Staphylococcus would not have the ability to transport peptidoglycan precursors, leading to the breakdown of the cell wall. (2) a gain of function mutation of autolysis genes in E. coli would lead to the breakdown of the cell because peptidoglycan sugar bonds would break down faster than replacing them. (3) treatment of streptococci in an isotonic solution with penicillin would inhibit transpeptidation. the cell would not be able to elongate because there would be no link between NAM and NAG pentapeptide to the already-existing bond

diagram the process of a gram stain.

(1) flood the heat-fixed smear with crystal violet so all cells are purple; (2) add iodine solution - all cells remain purple; (3) decolorize with alcohol so that gram-positives are purple, and gram-negatives are colorless; (4) counterstain with safranin so that gram-positives are purple and gram-negatives are pink/red.

Compare and contrast antibodies and vaccines. Which acts more rapidly? Which gives more long-term protection? How do each of these protect a patient from a disease? What is the protein that therapeutic anti-COVID monoclonal antibodies recognize?

*Antibodies* are produced by the body in response to combat a foreign invader. *Vaccines* are a biological preparation that provides active acquired immunity to an infectious disease. Immunity can be due to an addition of antibodies or infection of the recipient with weakened live viruses in order for the body to develop its own antibodies. Vaccines act more rapidly than antibodies. However, antibodies are more long-term. The protein that therapeutic anti-COVID monoclonal antibodies recognize is the spike protein.

Why is isoniazid a narrow-spectrum drug? How do daptomycin and platensimycin kill bacterial cells? Why are antifungal drugs typically more toxic than antibacterial drugs?

*Isoniazid* is a growth analog effective only against Mycobacterium; isoniazid interferes with synthesis of mycelia acid. *Doptomycin* is used to treat gran-positive bacterial infections by forming pores in the cytoplasmic membrane *Platensimycin* is a new structural class of antibiotics that is broad-spectrum; it is effective against MRSA and vancomycin-resistant Because fungal and animal cells are more closely related to each other and have very similar mechanisms within their cells, making it difficult to target specific differences between the fungi and animal cells.

how is the MIC and MLC calculated in lab? can the MLC be a lower dose than the MIC? why or why not?

*MIC* (minimum inhibitor concentration) is tested by diluting antimicrobial agents into different test tubes and looking to see the lowest concentration at which there is no growth. *MLC* (minimum lethal concentration) is tested by plating cultures from clear test tubes from the dilutions to see which concentration there is no longer growth at.

What is variolation?

*Variolation* was the method of inoculation first used to immunize individuals against smallpox. The idea is to deliberately infect a patient in order for them to form resistance (antibodies).

In your own words, define antibiotic resistance.

*antibiotic resistance* is the ability of a microbe to resist the effects of a chemotherapeutic agent to which it is normally sensitive.

how does an archaeal cytoplasmic membrane differ from a bacterial cytoplasmic membrane?

*archaeal*: ether links, isoprene tail *bacterial*: ester links, fatty acid tail

compare and contrast brightfield, darkfield, and phase contrast microscopy and give an example of each.

*brightfield*: the most common type of light microscope, often requires dyes to improve contrast *darkfield*: a stop is used to block light from hitting the specimen directly, creating a dark background, allowing living specimens to be seen *phase contrast*: called the phase ring, resulting in a dark image on a light background; produces high-contrast images

compare and contrast defined, complex, differential, and sensitive media. what are the advantages of each?

*defined*: known concentration of every molecule and compound in the media (exact composition of molecules) *complex*: chemically-undefined media (provides nutrition to bacterial cells that we do now know what we are providing) *differential*: allows growth of different organisms and shows different reactions by turning organisms different colors *selective*: only allows target microbes to grow

compare and contrast differentiation and reproduction

*differentiation*: cells are modified to perform specialized functions *reproduction*: the production of new cells

how do early proteins differ from middle and late viral proteins? which type of proteins are made and what is their function?

*early proteins*: enzymes needed for DNA replication and transcription (e.g., proteins that modify host RNA polymerase to "steal it"). *middle and late proteins*: head and tail proteins and enzymes required to release mature phage particles... 1. additional RNA and polymerase-modifying proteins 2. viral head and tail proteins 3. enzymes for breaking down peptidoglycan to release new virions from the cell

differentiate between high-affinity and low-affinity transporters. which are quickly saturated? which work best at high solute concentrations? are transporters typically specific or general in their substrates?

*high affinity*: become saturated when their target is at relatively low concentrations *low affinity*: work best when target is at high concentrations high affinity transporters are more quickly saturated low affinity transporters work best at high solute concentrations transporters are specific to their substrates

what are hopanoids and what is their function?

*hopanoids*: bacterial membrane lipids that act as a stiffening agent to reinforce membrane stability (resemble steroids)

how do ionizing and non-ionizing radiation kill microbes? what items are typically treated with ionizing radiation?

*ionizing* radiation breaks down DNA by killing through all surfaces. *non-ionizing* radiation kills microbes only on the surface by creating abnormal bonds in the DNA items treated with ionizing radiation include x-Rays, UV light, IR light, and heat/radio waves

how do bacterial cells react to hypertonic, isotonic, and hypotonic solutions? which of these conditions does a cell wall protect against?

*isotonic*: concentration inside the cell and outside the cell are the same; has no effect *hypertonic*: concentration is higher in the surroundings of the cell compared to inside the cell; causes the water from inside the cell to leave, so the cell shrinks and dies *hypotonic*: concentration is higher inside the cell compared to outside the cell; water rushes into the cell, causing it to swell and lyse, killing the cell the cell wall protects a cell from bursting in a hypotonic solution

compare and contrast macronutrients and micronutrients. what is each used for?

*macronutrients*: required in large amounts; needed for ion function *micronutrients*: nutrients needed in small amounts; needed for enzyme function

differentiate between resolution and magnification.

*magnification* is the capacity of a microscope simply to enlarge the image; these images can still be unclear. *resolution* distinguishes two adjacent objects as distinct and separate, therefore clearing up the image.

define, in your own words, the properties that ALL cells share: metabolism, growth, evolution.

*metabolism*: cells obtain nutrients from their environment and are converted to other materials for survival and waste *growth*: DNA is converted to proteins which are used to make new cells via use of proteins *evolution*: modification of cell properties over time from change in gene sequence and frequency

identify three separate factors that control the generation time of bacterial cells.

*nutrient availability*: well-fed bacteria reproduce faster than starved bacteria *species/genetics*: based on structural components *temperature*: warmer temperature increases reproduction but only to a certain point

what are three major functions of the plasma membrane? describe them.

*permeability barrier*: prevents leakage, allows certain things in and certain things out *protein anchor*: site where proteins participate in transport, bioenergetics, and chemotaxis *energy conservation*: site of generation and dissipation of the PMF

what are the 3 basic means to selectively move nutrients into a cell?

*permeases*: substrate-specific carrier proteins dedicated periplasmic nutrient-binding proteins membrane-spanning protein channels or pores

compare and contrast simple transporters, group translocation, and ABC transporters. what provides energy for these active transporters?

*simple transporter*: molecules move from high to low concentrations via anti-porter or symporter. the molecule that powers the transport is the one that moves from a high to low concentration (PMF). *group translocation*: uses energy from PEP to attach a phosphate to specific sugars via binding proteins (enzyme I and enzyme II) *ABC transporter*: binding proteins are involved and energy comes from ATP

how do soaps, triclosan, and alcohol affect plasma membranes and viral envelopes?

*soap* is amphipathic, meaning it has both polar and non-polar regions. this disrupts the phospholipid bilayer. *triclosan* is a competitive inhibitor of the enzyme that adds to the tails of the phospholipids. hand-sanitizer works because the alcohol dissolves lipids. hand-washing works against COVID-19 because SARS-CoV2 is an enveloped virus, meaning it has a lipid coat that be disrupted by soap.

compare and contrast antisepsis, disinfection, sanitation, and sterilization. do surgeons sterilize human skin prior to surgery?

*sterilization*: killing all living organisms *disinfection*: killing/removing pathogens from INANIMATE objects *antisepsis*: killing/removing pathogens from LIVING TISSUES *sanitation*: reducing the microbial population to a safe level surgeons probably do not sterilize skin, they most like perform antisepsis.

what are tissue tropism and species specificity? what stage of the life cycle determines both?

*tissue tropism*: the cell and tissues of a host that support growth of a particular virus or bacteria. *species specificity*: the restriction of a characteristic or response to the members of one species; it usually refers to that property of the immune response which differentiates one species from another on the basis of antigen-recognition. the *attachment phase* of a viral replication cycle determines both species specificity and tissue tropism.

Describe which viruses have ribosomes, lysins, hemagglutinin, neuraminidase, a lipid layer, RNA replicase, spike proteins, and reverse transcriptase (RT). Where does the viral envelope come from? Are reverse transcriptase (RT) and RNA-dependent RNA polymerase enzymes provided by the host cell or the viral particle? Why is that the case?

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Draw a viral particle, labeling the nucleic acid, capsid and envelope. Differentiate between enveloped and naked, single-stranded and double-stranded viruses, positive- and negative-stranded, RNA and DNA viruses (in terms of durability, mutation frequency, formation of a provirus, recombination, and which viruses are commonly single-stranded and which are most-commonly double-stranded).

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why do microbiologists frequently perform serial dilutions to determine the CFUs in a growing culture? why do you typically plate 0.1 mL rather than 1 mL on your agar plates?

1 mL is too much solution; you wouldn't be able to count all of the CFUs and see the total amount of cells on the plate.

give 2 real-world examples of biofilms in nature.

1. biofilm forming on catheter 2. biofilm on an old pipe; when used, it will cause disease from diverse biofilm formation

looking at the lambda life cycle, compare and contrast the lambda repressor and cro proteins.

1. cI protein (lambda repressor): causes repression of lytic events; represses cro protein 2. cro protein: activates lytic events and represses cI protein

what are three basic life functions all cells need to perform to remain living, viable cells? what structures perform each of these three functions? what aspects of mycobacteria's structure contribute to its slow growth?

1. cellular integrity, energy-harvesting, and gene transmission 2. the 3 structures are: plasma membrane, DNA, & enzymes 3. the waxy coat of mycobacteria contributes to its slow growth

describe four differences between endospores and vegetative cells.

1. endospores have high levels of calcium 2. endospores have a very low water content 3. endospores are resistant to lysozyme 4. the enzymatic activity, respiration rate, and synthesis of macromolecular organisms is very small or absent in endospores

what is Pseudomonas aeruginosa and how is it relevant to human health and biofilm formation?

1. forms tenacious biofilm containing polysaccharides that increase pathogenicity and prevent antibiotic penetration 2. opportunistic, infects blood, lungs, urinary tract, ears, skin, and causes cystic fibrosis 3. forms in burn patients + cystic fibrosis

what is the "great plate count anomaly?" give multiple reasons why this anomaly exists.

1. microscope counts and turbidity measure a sample count that is always more than what is recoverable on plates 2. Petroff/turbidity counts dead cells; alive, but not dividing 3. standard plate counts only count live CFU 4. standard plate counts only count bacteria that can be cultured

Would microbe that shows no zone of inhibition would be considered resistant or susceptible to a given antibiotic? Why do scientists use a chart to determine the susceptibility or resistance of a microbe to antibiotics?

1. no zone of inhibition would be considered as resistant to the antibiotic 2. a large zone of inhibition would mean that the antibiotic is working, so the bacteria would be considered susceptible to the antibiotic 3. scientists use a chart to determine the susceptibility or resistance of a microbe to antibiotics because it helps set guidelines for resistant, intermediate, and susceptible agents that can be used to treat different diseases/infections, etc.

You make a chart measuring concentration of bacteria (CFU/mL) vs time and see that the slope of organism 1 is 0.1, the slope of organism 2 is 0.07, and the slope of organism 3 is 0.15. Put these organisms in order from fastest growing to slowest growing. Assume the time frame and concentration measurements were the same for all 3 organisms.

1. organism 3 (0.15) 2. organism 1 (0.10) 3. organism 2 (0.07)

Why is oxygen toxic to some organisms? What enzymes do aerobes have that anaerobes lack? Draw the growth of obligate aerobes, facultative anaerobes, obligate anaerobes, microaerophiles, and pure fermenters in the test tube. Compare and contrast fermenters and microaerophiles in terms of their use of oxygen and the relative toxicity of oxygen for each.

1. oxygen makes a lot of toxic byproducts that some microorganisms cannot handle 2. enzymes that anaerobes lack are catalase and superoxide dismutase (SOD) 3. fermenters can handle oxygen and they can grow without it, too 4. microaerophiles cannot live without oxygen, for the most part, and do not live very well in high-oxygen; they like to be in-between the two.

What is salvarsan and what is the active segment of this drug and what was it used to treat? Why doesn't sulfonamide harm a human host, but will kill bacteria?

1. salvarsan, also known as arsphenamine, is a drug that was introduced at the beginning of the 1910s as the first effective treatment for syphilis and African trypanosomiasis 2. all cells require folic acid and it can diffuse easily into human cells, but the vitamin cannot enter bacterial cells, and thus bacteria make their own. 3. sulfa drugs are bacteriostatic, i.e., they inhibit the growth of multiplication of bacteria but do not kill them. they act by interfering with the synthesis of folic acid (folate), a member of the vitamin B complex present in all living cells

compare and contrast viruses, prions, viroids, bacteria, protozoa, fungi, helminths, and archaea in terms of relative size, nature of metabolism, location of metabolic process, and nature of their nucleic acids, key traits, and indicate whether each is a prokaryote, eukaryote, or acellular.

1. virus - acellular; ssDNA, dsDNA, ssRNA, or dsRNA; 0.01-0.2 microns 2. prion - acellular; nu nucleic acids; 0.01-0.2 microns 3. bacteria - prokaryote; dsDNA; 5-10 microns 4. protozoa - eukaryote; dsDNA; 20-100 microns 5. fungi - eukaryote; dsDNA; 20-100 microns 6. helminth - eukaryote; dsDNA; 20-100 microns 7. archaea - prokaryote; dsDNA; 5-10 microns

calculate the end concentration if you were studying a virus whose burst size was 50 PFU and it went through 4 replication cycles? which sample would have more pathogens?

50*4 = 200 the last sample would have the most pathogens

Phase II of vaccine development

A group of 25-100 recipients are given the drug. They're treated using the same dose and method found to be the safest and most effective from Phase 1. Everyone is given the same dosage and no placebos are used.

how does COVID-19 cause disease? why do you think immunosuppressants are given to patients with severe COVID-19 infections?

COVID-19 causes an overactive immune response in the lungs and brain. a cytokine storm occurs where WBCs are caught in a positive-feedback loop, amplifying the response and damaging nearby tissues. the excessive swelling in the enclosed cranium and/or lungs is not compatible with many human life functions.

peptidoglycan has D-amino acids. why is this important to its structure and function?

D-amino acids are not typically used in proteins, so they will be resistant to an enzyme attack, the NAM-NAG subunits of peptidoglycan are similar in most bacteria, while the peptide portion varies greatly

how can DNA be exchanged between microbes?

DNA is exchanged between cells via horizontal gene transfer

compare and contrast the Stanford E. coli experiment and the Griffith experiment. what cellular structures were demonstrated to be virulence factors by these experiments?

E. coli uses pili to attach to the intestinal surface. in a 1998 *Stanford experiment*, test subjects were given normal E. coli and got sick. a second group that got the E. coli without pili (a genetic mutant lacking the genes for pili) did NOT get sick. this is part of Koch's postulates: disease is associated with a molecule, not simply the bacteria that it is infecting. The *Griffith Experiment* demonstrated that the capsule is a virulence factor. it also demonstrated that genetic information can be transferred horizontally via transformation.

Who were Florey, Chain, Fleming and Albert Alexander and why are they important to microbiology?

Florey and Chain were the scientists who followed up most successfully on Fleming's discovery of penicillin, winning him the 1945 Nobel Prize in Medicine and Physiology.

what type of virus is HIV? what disease does it cause and how is it treated?

HIV is an enveloped retrovirus. HIV targets CD4+ T-cells and causes AIDS. AIDS is treated by HAART (highly-active antiretroviral therapy). this inhibits reverse transcriptase (RT), protease, and integrase (viral enzymes).

what disease(s) doo human papillomaviruses cause?

HPV causes warts, cancers, herpes, chickenpox, flu, norovirus, etc.

how does Haemophilus harvest iron?

Haemophilus harvests iron from RBCs by shaking the iron out of the hemoglobin

who was Louis Pasteur and how did he cure "sick wine?" what was his training? did his experiment with the swan-necked flask support or disprove spontaneous generation?

Louis Pasteur was a French chemist in the 1800s that was hired to cure "sick wine." he fixed the problem of contaminating bacteria by heating. Pasteur's swan-necked experiment disproved the theory of spontaneous generation.

Can OD readings distinguish between bactericidal and bacteriostatic drugs? Why or why not?

OD readings can NOT distinguish between bactericidal and bacteriostatic because the cell structures are still there to refract the light in the spectrophotometer.

would you expect a patient that was homozygous for dysfunctional CCR5 allele to be more or less susceptible to HIV? why? what evidence is there for this conclusion and how do you know if someone is homozygous for this receptor?

One of the standard treatments for acute myeloid leukemia (AML) is irradiation followed by a stem cell transplant (SCT). they found an individual with compatible bone marrow, who also happened to be homozygous for the dysfunctional CCR5 allele. The patient now had WBCs that lacked one of the proteins that HIV uses for attachment and entry. He has been HIV free for 20+ months and treatment with HAART was discontinued. The caveats include donor-matching, risks/complications with transplants, and immunosuppressive drugs being needed to maintain transplant health.

Identify 7 different cellular targets of antibiotics? Are drugs that target the cytoplasmic membrane more or less toxic than those that target peptidoglycan? Explain.

RNA polymerase, DNA gyrase, mRNA, ribosome, chromosome, cytoplasmic membrane, cell wall. Drugs that target the cytoplasmic membrane are more toxic than those that target the peptidoglycan. Drugs that target the cytoplasmic membrane will target the phospholipids in both the bacteria and the human cells of cytoplasmic membranes. The drugs that attack the peptidoglycan in the cell wall will only target bacterial cells and not the human cells that lack a peptidoglycan cell wall.

Phase I of vaccine development

Recipients receive VERY small dosages. They are then watched closely, and if there are only minor side effects, the next few recipients receive a higher dose. This goes on until side effects are very minor for even high dosages. This continues until doctors find a dose that is most likely to work while having an acceptable level of side effects.

who was the first individual to see a eukaryotic cell? who was the first person to see a prokaryotic cell? what other discoveries were made by these first microscopists?

Robert Hooke was the first to see a eukaryotic cell and coined the term. Antoni van Leeuwenhoek was the first to see prokaryotic cells (bacteria) that he called animalcules. also coined the term spermatozoa and believed them to be parasites, hence the origin of their name.

who was Robert Koch and why is he considered a co-founder of microbiology? diagram Koch's postulates. can Koch's postulates be used in every situation? why or why not? how do Koch's postulates apply to COVID-19 testing?

Robert Koch was a German physician that studied anthrax in mice. he found a way to culture bacteria (petri dish, role of agar) and developed a process to link diseases to bacteria. these "rules" are known as Koch's postulates. these postulates can only be used in certain situations, depending on the environment and laboratory tools available. not everything grows in culture (e.g., leprosy) and not everything has a useful animal model (human diseases only). Koch's postulates help us identify where COVID-19 came from and how we can test for COVID-19 in humans.

what type of virus is SARS-CoV2? what disease does it cause? what other viruses are in the same group? what are the receptors for SARS-CoV2?

SARS-CoV2 is a positive, ssRNA strand with a relatively large genome. it causes upper respiratory infections. SARS-CoV2 is a coronavirus (1 of 7 known coronaviruses). it causes COVID-19. other viruses in the same group include SARS and MERS. SARS-CoV2 uses ACE-2 and TMPRSS as co-receptors: the lungs, blood vessels, and kidneys lead to high levels of ACE-2.

which protein(s) is/are most vaccines against SARS-CoV2 targeting?

SARS-CoV2 vaccines target four major structure proteins: (1) spike proteins (*S*): embedded on virion surface (2) membrane proteins (*M*): embedded on virion surface (3) envelope proteins (*E*): embedded on virion surface (4) nucleocapsid protein (*N*): binds viral RNA inside the virion

Phase III of vaccine development

Several hundred patients are used across the whole country. The same treatment as the one in Phase 2 is given to the recipients. This time, some are even given a placebo. The recipients are closely watched and it is recorded what % of dosage and placebo recipients acquire the disease.

Which steps of the infection cycle are being targeted by re-purposed drugs? Why are researchers testing out existing drugs instead of making new therapeutic agents?

The main reasons that researchers are using existing drugs instead of making new therapeutic agents are because we don't necessarily know how, it is expensive, and we already have the groundwork laid out. The steps of the infection cycle are being targeted by re-purposed drugs include: 1. attachment inhibition: *TMRSS2* 2. entry alteration: *chloroquine* 3. prevention of viral protein formation: *lopinavir* 4. prevention of viral RNA polymerization: *remdesivir* 5. block hyperinflammation: *dexamethasone*

Calculate the therapeutic index (T.I.) of an agent whose toxic dose is 100 ug and effective dose is 50 ug. Which would be safer, an antibiotic with a T.I. of 50 or one with a T.I. of 5?

Therapeutic Index (T.I.) = TD50 / ED50 T.I. = 100 µg / 50 µg = T.I. = 2 An antibiotic with a T.I. of 50 would be safer than an antibiotic with a T.I. of 5 (smaller LD is more dangerous). The higher the lethal dose, the larger chance we have at living. Both numbers are divided by the same ED50, so we would find that the T.I. of 50 is MUCH SAFER.

You have a flask from an overnight culture and take 1 mL from this flask and put it into 9 mL of PBS to dilute it (tube 1), you then take 1 mL from tube 1 and put that in a tube with 9 mL of PBS to make tube 2. You take 1 mL from tube 2 and put it in a tube with 9 mL of PBS to make tube 3. You take 1 mL from tube 3 and add it to tube 4 with 9 mL of PBS. Finally, you take 0.1 mL from tube 4 and plate it on an agar plate. The next day, you count 218 colonies on the plate. What was the concentration of bacteria (in CFU/mL) in the original overnight flask? Show your work.

Tube 1 dilution = 1:10 2 = 1:100 3 = 1:1000 4 = 1:10,000 CFU/mL = (# colonies * dilution factor) / volume of culture plate CFU/mL = (218*10^4)/0.1 mL = 2.18*10^7 CFU/mL

What is the idea that masks may work to variolate a population? Does it have strong evidence to support it?

Wearing face masks can reduce the amount of virus that a susceptible person comes into contact with, leading to less severe diseases if the person does become infected. Such mild infections are less likely to result in death and complications, while inducing immunity to the disease at the same time. This does have some evidence, but it is not 100% supported.

would a cell that lacked siderophores grow better or worse in an iron-poor environment?

a cell that lacks siderophores would grow *worse* in an iron-poor environment. they would be less resistant because their job is to keep iron away from pathogens so that they are unable to use it as energy (host side).

would a host that lacked transferrin or lactoferrin be more or less resistant to infection? why?

a host that lacked transferrin would be less resistant to infection. the iron-binding protein is found in blood, which keeps iron away from pathogenic siderophores and transfers it to WBC macrophages for immune protection.

would an environment that lacked dentrifiers have more or less useful nitrogen in the soil?

a lack of dentrifiers would result in more useful nitrogen because nitrate is not able to be converted into nitrogen gas, which is unusable nitrogen.

Can a person become resistant to antibiotics? Explain.

a person cannot become resistant to antibiotics in general, no; however, after constant use of a specific antibiotic, the body can become immune to that certain antibiotic, thus leading the ineffectiveness of that antibiotic on that person

what is pure culture? how does a colony form? are most microbes found in pure culture in nature? explain.

a pure culture is a colony of microbes that originated from an individual cell. a common way to accomplish this is using the four quadrants technique to isolate microbes into individual colonies to attain a pure culture. this single microbe will divide exponentially, creating a larger and larger colony that will eventually be seen with the naked eye. pure microbes are not naturally found in nature; most microbes are found in mixed populations

compare and contrast a simple and differential stain. what do both stains do to the microscope image? what can we identify with a simple stain? give examples.

a simple stain colors everything the same color. we can see cell morphology and cell walls. differential stains color different bacteria different colors. the differences in cell structure lead to different binding characteristics from the cell to the dye or vice versa. both stains do not change anything about the microscope except the image and ability to detect microscopic differences in bacterial structures.

what if you decolorize with water instead of alcohol?

all cells would be left purple

what would happen if you reverse the safranin and crystal violet?

all cells would be left purple

if you stain staphylococcus (gram-positive cells), but remove their peptidoglycan layer first what color would they be? why?

all cells would be pink, since the peptidoglycan layer cannot be stained purple

are archaea and bacteria closely related? explain.

archaea and eukaryotes are more closely related than archaea and bacteria. archaea and eukaryotes share more ancestors on the tree of life (they extend from the same central branch). so ultimately, no, archaea and bacteria are not very closely related.

what environmental conditions would you expect to favor archaea with tetra-ether monolayers? why?

archaea with tetra-ether monolayers would favor high-temperature environments because they would be considered thermophiles and resist membrane-melting

what is burst size and how is it calculated? which cells (prokaryotic or eukaryotic) typically yield more viruses? do viruses burst bacterial cells by overfilling them? what evidence is there for this?

assume 1 virus per bacterial call and that the cell will lyse. the viruses started at approximately the same time, so they'll burst at about the same time. if you had 100 bacteria and 10,000 phage appear at release, the burst size is 100 (or 100 new virions per single cell infected). this number varies greatly, but eukaryotic cells generally yield more virions. the cell doesn't burst like a balloon... T-phage with ~50 nm diameter shows burst sizes of ~200 in an E. coli cell. Those 200 phage represent ~2% of the E. coli volume.

why do cells need iron?

bacteria and pathogenic cells need iron to grow.

how does filtration limit the spread of microbes? why is it ineffective against viruses?

bacteria are big and will be filtered out of a solution; viruses are very, very tiny.

when you see the phrase "bacterial growth" or "viral growth," does this mean larger organisms or more individuals in the population? how does that differ from "growing plants" or "growing animals?"

bacterial growth indicates an increase in the # of cell. it differs from the "growing animals" because those terms indicate growth in size, not number

what is meant by bacterial growth?

bacterial growth refers to growing population, not a singular bacterium getting larger itself

why is it important for a bacterial cell to be small? what advantages does the small size give to prokaryotic cells?

being smaller is better for: (1) more nutrients in, (2) more waste out, (3) shorter generation time, (4) larger populations, and (5) faster mutation rate and evolution

differentiate between planktonic and biofilm bacteria in terms of gene expression and antimicrobial resistance.

biofilm bacteria: help create resistance to antibiotics, drying out, and immune system mechanisms

predict the impact of a loss of function mutations in Pseudomonas aeruginosa's quorum-sensing systems on the bacteria's survival in vitro and in vivo, with and without antibiotic treatment.

block quorum-sensing, it reduces the load of bacteria, and it would die from antibiotic treatment

compare and contrast the flagella found in gram-negative and gram-positive cells. what powers the rotation of flagella?

both gram-negative and gram-positive cells have filaments, hooks, basal bodies, Mot proteins, and flagella. gram-positive bacteria lack outer membranes; no LPS, no P or L ring; the peptidoglycan layer is much larger, meaning the basal body is much larger. the PMF powers flagellar rotation and bacterial movement via Mot proteins.

what function does a capsule serve for a prokaryotic cell? how does a capsule differ from a slime layer?

capsules are firmly attached to prokaryotic cells, while slime layers are not. the polysaccharide coating... 1. provides the extracellular matrix for biofilm formation 2. provides stickness 3. protects from engulfment 4. gathers water, so protects from desiccation

Explain the effects of soap, heavy metals, and ethylene oxide on bacterial cell structures.

cell membranes: *soaps* are amphipathic (having both polar and non-polar regions), so they will disrupt the phospholipid bilayer. proteins: *heavy metals* will irreversibly bind to proteins, often inactivating them (e.g., enzymes no longer work) ethylene oxide (EtO) chemical modified proteins and DNA by inactivating them

how do cells communicate with each other?

cells communicate via intercellular communication

what if you forget the iodine or to heat fix your cells?

cells would wash away

Given the capillary test for motility, the media had 20 CFU/mL in the capillary tube. Chemical A had 50 CFU/mL in the capillary tube. Chemical B had 3 CFU/mL in the capillary tube. Which chemical is an attractant and which is a repellent? How do you know?

chemical A is an *attractant* because it yielded more bacteria than the original media chemical B is a *repellent* because it yielded less bacteria than the original media

how are chickenpox and shingles related?

chickenpox and shingles are the same disease, but chickenpox is the name for the "first exposure." in this case, some viruses (chickenpox) can hide for decades and re-activate, coming back in different forms (shingles).

where did chloroplasts and mitochondria originate? what evidence for this is there?

chloroplasts and mitochondria are believed to have descended from ancient free-living prokaryotes that were absorbed into the membrane of a cell. the evidence for this is that both chloroplasts and mitochondria have their own DNA.

why is confocal microscopy an innovative technique, especially where biofilms are concerned?

confocal microscopy uses a computer to model cells in a biofilm, allowing it to determine the order of microbes from top to bottom

Write the Abbe equation and describe the impact of changing the wavelength of light, working distance, and using immersion oil on the resolution of a microscope.

d = resolution; d = 1/2(ƛ) / n(sinΘ) Lambda = wavelength of light; blue is shortest n is determined by the refractive index of the material between the lens and the slide; dry lens "n" = 1; oiled lens "n" = 1.56 Θ = 1/2 of the cone of light entering the objective Shorter focal length means a larger Θ angle Larger denominator (n(sinΘ)) yields a smaller resolution "d" Light microscopy can be altered by changing the path of light slightly. We use three main types of microscopes in MICRO 302 and 201 labs. They include: Brightfield Darkfield Phase contrast (simply increases contrast) Immersion oil improves the resolution of the microscope by decreasing the wavelength of light (smaller lambda)

which phase does continuous culture prolong? how does continuous culture differ from batch culture? what is the effect of adding more nutrients on microbial growth rate? what limits this effect?

effect of adding more nutrients: increased growth rate, but only until a certain point; adding more nutrients when growth rate plateaus will wash bacteria away.

how is the sample itself the light source in fluorescent microscopy? how do dyes and antibody staining differ from using GFP?

either the cells have natural fluorescent substances such as chlorophyll, or they are injected with fluorescent due. DAPI does not kill cells, but GDP does kill the specimen.

how does microbial generation time influence their speed of evolution?

evolution occurs quickly because microbes are small, so their generation time is extremely short

can facilitated diffusion move molecules from low to high concentration? why or why not?

facilitated diffusion moves molecules from high to low concentrations (i.e., *with* the concentration gradient) because it is a passive form of transport that does not require energy.

how is fermentation an important process in food production? what does yeast do for bread and beer?

fermentation is an important process in food production and can be used to make bread, wine, yogurt, and more. yeast in bread causes the dough to rise, and in beer it produces alcohol, a major component of beer.

how do archaella differ from flagella? would the loss of a PMF impair the function of flagella, archaella, or both?

flagella are long, thin appendages or "whips." they have 3 different arrangements: polar, lophotrichous, and peritrichous. flagella increase or decrease rotational speed relative to strength of the PMF. archaella are essentially flagella, but for archaea. archaella are 1/2 the diameter of bacterial flagella and move by rotation, similar to flagella. they are composed of several different filament proteins with little homology to bacterial flagella. powered by ATP, not the PMF.

what is the function of a flagellum?

flagellum allow the cell to move

presence of LPS

gram-negative bacteria

presence of porins:

gram-negative bacteria and archaea

presence of N-acetyl muramic acid

gram-positive and gram-negative bacteria

presence of teichoic acid

gram-positive bacteria

presence of ether-linked fatty acids

gram-positive bacteria, gram-negative bacteria, and archaea

arrange the different types of microbes (viruses, prions, prokaryotic cells, eukaryotic cells, and helminths) in the correct order from largest to smallest. if you have a sieve or filter that allowed prokaryote cells to pass through, but retained the eukaryotic cells, would you expect most viral particles to pass through or be retained? explain.

helminths > eukaryotic cells > prokaryotic cells > viruses > prions most viral particles would pass through a filter that allowed prokaryotic cells to pass through but retained eukaryotic cells. most viral particles are smaller than most prokaryotic cells, so they would be small enough to pass through the filter

would you expect a cell that lacked RecA to favor a lytic or lysogenic pathway? why?

if a cell lacked RecA, it would favor the lytic pathway, because it would not be able to cleave the cI protein which causes repression of lytic events

if someone is born with more receptors, would they be more or less susceptible to the viral illness? less receptors? what evidence is there for this?

if someone is born with MORE receptors, they would be *more* susceptible to viral illnesses. if someone is born with LESS receptors, they would be *less* susceptible to viral illnesses. fewer receptors on host cells means less viral load, or the inability of a virus to infect different cells.

what would happen if you mutate the Enzyme I or Enzyme II system of a PTS transporter? why is group translocation advantageous to a cell?

if you lose Enzyme I function, it is likely lethal as it would prevent multiple sugars form entering the cell. if you lose Enzyme II function, it changes the sugars coming into the cell (so not lethal, but not good either). group translocation is advantageous because it provides energy-rich organic compounds that drive the transport event.

if you were trying to determine the metabolic inputs and outputs of each bacteria in culture, would you use complex or defined media? defend.

if you were trying to determine metabolic inputs and outputs of bacteria and culture you would use *defined* media because with this type of media, you are able to know exactly what you are putting in and what is coming out.

does starting with more bacteria in the initial inoculum give you more total bacteria in stationary phase of batch culture? why or why not?

in batch culture, to begin to run out of nutrients for the cells, they start to produce more waste. therefore, they are dying at the same rate at which they are reproducing. so no, it does not give you more bacteria in the stationary phase. the stationary phase is where things begin to level off.

why are endospores of concern to food microbiologists? how did climate change contribute to an anthrax outbreak in 2016?

in food microbiology, endospores are seen in the deadly disease *botulism*. in 2016, thawing of the permafrost in Siberia allowed anthrax endospores to germinate and grow on an infected reindeer. more than 2000 reindeer were infected and nearly 250,000 reindeer were killed to stop anthrax.

why is isolating an organism's nucleic acid important? what are the possible configurations of a virus? can bacteria have an RNA genome? single-stranded genome?

isolating a nucleic acid means we can determine if it has DNA or RNA, if it is circular or linear, if it is single- or double-stranded (viruses), its sequence (to track spread), and its unique proteins (used for testing). the concept that invisible organisms can cause diseases is known as "germ theory."

calculate the surface area to volume ratio of a cell with a diameter of 2 µm and another cell with a 10 µm diameter. which is preferred, a large or small surface area to volume ratio? why?

it is better to have a larger SA:V ratio because there is a more rapid exchange of nutrients. therefore, small diameters with larger surface areas are preferred. SA:V → SA/V SA = 4πr2 V = (4/3)πr3 SA = 4π(22) = 50.27 V = (4/3)π(23) = 33.51 SA/V = 1.5 SA = 4π(102) = 1256.64 V = (4/3)π(103) = 4188.79 SA/V = 0.3

evaluate the relative growth rate of a microbe growing in culture vs "in the wild;" which would grow faster? why?

lab cultures grow faster than microbes found in nature because microbes in nature must compete with one another to obtain necessary nutrients and space to grow. in lab, microbes are given "special treatment" that optimizes their growth.

how is lysogeny maintained? if the lambda repressor protein were to be inactivated by mutation, would a virus be virulent or temperate? what general conditions induce a lytic pathway?

lysogeny is maintained by phage-encoded repressor proteins. the inactivation of repressors induces lytic stage, and in general, bacterial cell stress induces the lytic pathway. if the lambda repressor protein were to be inactivated by mutation, the virus would be virulent because it eliminates the prophage stage (temperate viruses become prophages).

what does lysozyme do to peptidoglycan? how does penicillin affect peptidoglycan? do both penicillin and lysozyme kill non-growing cells? why or why not?

lysozyme breaks the Beta 1-4 links between sugars. penicillin inhibits the transpeptidase enzyme needed to make cross-links. penicillin prevents the formation of new peptidoglycans, it does not affect established peptidoglycans much, so non-growing cells are much less sensitive to penicillin.

When and how is ethylene oxide used as an anti-bacterial agent?

materials are sterilized by ethylene oxide (EtO). EtO is a powerful alkylating agent - chemically modifying proteins and DNA drawbacks of EtO include that it is a carcinogen and explosive/flammable approximately 50% of all medical devices, including catheters and surgical mesh, in the US are sterilized using EtO.

are all microbes prokaryotes? are all prokaryotes microbes? why is the term microbe rather vague?

microbe comes from the Greek prefix "micro-," meaning small. so, when we are referring to something that is "micro," we are saying that it is small and cannot be seen with the human eye, not all microbes are prokaryotes, such as bacteria and fungi particles. due to their size, all prokaryotes would be considered microbes.

why are microbes a problem in food microbiology? give 2 reasons. is spoilage the same as food-borne disease?

microbes are a problem in food due to the health issues that they can cause, sometimes even leading to death. microbes can also contaminate large amounts of food, leading to spoilage. spoilage is not the same as food-borne disease. spoiled organisms are *dead*; spoiled organisms do not cause life-threatening infections because of this. on the other hand, food-borne diseases arise from live pathogens in our food, and consequently will make you sick and can even kill you.

how are microbes important in agriculture? particularly, to soybean and dairy farmers?

microbes are important in agriculture and provide many uses. one of the major uses being that they aid in the nitrogen-fixation of soil. this helps us to regulate the natural nitrogen cycle.

why are microbes important in the production of ethanol from corn or switchgrass?

microbes are important in the production of ethanol because they are the means that we are able to ferment corn or switchgrass with. by breaking down the glucose from the plants, they produce ethanol as a byproduct that we can use as a source of energy.

why are our resident microbes important to human health? give three different examples of their influences.

microbes are important to human health because they help us digest our food, change the way drugs are absorbed in our bodies, and can cause diseases.

what % of the time that the earth has existed were microbes the only life on the planet? which came first: free oxygen in the atmosphere, or microbes? what happened to most life on earth during the "oxygenic revolution?"

microbes have been the only life form on earth for about *65-80%* of the earth's existence. microbes came long before free oxygen. during the "oxygen revolution," nearly all of the living organisms on earth died because they were all anoxygenic phototrophs.

How do we define microbial death? If you had 10^5 CFU/mL and heated this culture for 20 minutes and found 10^3 CFU mL at the end of the procedure, what is the D value of this heating protocol? You calculate a different protocol to have a D value of 8 minutes and another protocol with a D value of 15 minute, which is the better protocol to kill microbes? Explain.

microbial death: failure of microbes to grow in conditions that they would normally be able to do so 10 minutes 8 minutes, it kills 90% of microbes at almost twice the rate.

Which works better - moist heat or dry heat? Which are more resistant to killing - vegetative cells or endospores? Why is pressure added to an autoclave? How does cold affect microbial growth?

moist heat works better than dry heat, as it penetrates better and denatures proteins. endospores are more resistant to killing. pressure in an autoclave allows the temperature of water to get very hot (121 C). cold temperatures only slow down the bacteria activity, which actually preserves microbes.

in general, which molecules pass most freely? charged or uncharged? larger or smaller molecules?

molecules that pass more freely are smaller, uncharged molecules

what is the relative abundance of microbial vs. visible life? are most of these cultured in lab? how do we build the "universal tree of life?"

most organisms on earth are microbial and uncultivable (hard to separate into pure substances because they occur in mixed environments). we use red dots to represent microbes that we know are there but are not cultured on the tree of life. the tree of life is built on rRNA, so we can isolate and analyze the DNA to generate a phylogenetic tree for the bacteria, archaea, and eukarya.

how do mycobacterial cell envelopes differ from most bacterial cell envelopes? what are the advantages of having such an unusual cell envelope? how does this cell envelope affect the growth rate of mycobacteria?

mycobacteria have a complex, waxy envelope. the waxy coat makes it hard to get nutrients in and this slow growth. the waxy coat also protects the cell, making mycobacteria hard to kill.

would penicillin be effective against mycoplasmas? why is it important that mycoplasmas have cholesterol?

mycoplasmas lack peptidoglycan. they also have no cell wall; they have cholesterol in their membrane to strengthen it. walking pneumonia is caused by a mycoplasma, so it cannot be treated with penicillin. mycoplasmas cannot be treated with penicillin because because they lack a cell wall, which is what penicillin targets.

was Robert Koch's treatment for tuberculosis (TB) an actual remedy for the disease? why were so many people deceived? who debunked this treatment?

no, Koch's "remedy" was simply to inject people with TB and allow their immune systems to fight the disease via generation of antibodies. people got really, really sick but then eventually recovered. Arthur Conan Doyle debunked this treatment.

can you use penicillin to treat chickenpox? why or why not?

no, penicillin cannot be used to treat chickenpox. penicillin prevents bonds made in the cell wall to form. viruses do not have a peptidoglycan layer, nor do they have a cell wall, so penicillin would not have any effects on a viral infection like chickenpox.

are persister cells endospores?

no, persister cells are NOT the same as endospores.

can we grow viruses on blood agar? why or why not?

no, you cannot grow viruses on agar plates; they are obligate intracellular parasites, so you need to give them a place to grow in target cells

can a light microscope be used to examine prions or viruses? why or why not?

no. germ theory does not prove that bacteria, viruses, and prions can be seen by light microscopy. in order to examine viruses and prions (very, very small particles), electron microscopy must be used.

presence of diaminopimelic acid (DAP)

none

presence of dipicolinic acid (DPA)

none

presence of hami

none

what disease does norovirus cause?

norovirus causes food poisoning

Imagine you were sloppy when making some deviled eggs and accidentally introduced 100 CFU's Salmonella into the eggs while preparing them. If the generation time is 30 minutes at room temperature and 2 hours in the refrigerator, how many Salmonella would be in your eggs after 5 hours on a picnic table (room temperature)? How many Salmonella would be in the same plate of eggs that was held in the refrigerator. Explain to a party organizer why the cold picnic food needs to be held on ice.

number of colonies = 100 (300 minutes for 5 hours) N = 300/30 = 10 100 • (2*10) = 10,000

which cells have dipicolinic acid? do gram-negative or archaeal cells form endospores? is the formation of an endospore a form of reproduction, differentiation, or both?

only certain gram-positive bacteria can form endospores (no gram-negative, archaea, or eukarya). 1. endospores form from nutrient deprivation, stress, DPA drying out the cell to stabilize DNA, and small acid-soluble proteins (SASPs) drying DNA to reserve energy 2. endospores are formed via *differentiation*, not reproduction

What are 6 different molecular mechanisms for this resistance (in your own words).

organism lacks structure the antibiotic inhibits organism is impermeable to antibiotic organism may modify the target of the antibiotic organism can inactivate the antibiotic organism may develop a resistant biochemical pathway organism may be able to pump out the antibiotic (efflux)

would penicillin work on archaea? why or why not?

penicillin would not work against archaea, either, because the peptide cross-links are Beta 1-3 links, not Beta 1-4 links

Which of these mechanisms explains why physicians do not give penicillin to patients with mycoplasma pneumonia? Which mechanism would most likely be used by bacteria developing resistance to sulfa drugs?

physicians do not give penicillin to patients with mycoplasma pneumonia because the organism is impermeable to the antibiotic; the thick, waxy coat of mycoplasma inhibits the ability of penicillin to disrupt the cell walls the mechanism that would most likely be used by bacteria developing resistance to sulfa drugs would be developing a resistant biochemical pathway or inactivating the antibiotic.

compare and contrast pili from flagella. which structure is important in DNA transfer.

pili are few in # and longer than fimbriae and are involved in the use of labeled viruses. flagella allow cells too move and look like hair-like spindles that run and tumble for movement (counter-clockwise direction is running, clockwise direction is tumbling); Leifson-stain stains flagella red-brown.

how do quorum-sensing, horizontal gene transfer, and differentiation affect the ability of microbes to cause disease?

quorum-sensing is used by the microbes to "count" how many other microbes it is surrounded by, and attempts to overwork the host's defense mechanism by overwhelming it with sheer numbers. horizontal gene transfer is used as a way to differentiate between other cells, and possible evolve a resistance toward the host's defense mechanisms.

diagram the process of attachment and describe molecules that are typically used as viral receptors.

receptors have functions for the host cells (e.g., flagella, pili, immune molecules, etc.). these receptors can be different macromolecules. once attached, the viral tail fibers contract to inject the viral genome into the host cell.

How does salt impact microbial growth and how do bacteria adapt to living in high salt conditions? Why is salt used in jerky and sugar in jam? If a cell gained a gene that allowed it to produce more or different compatible solutes, what environments could it live in better? Why are weak acids used as food preservatives? What is a sodium motive force and which bacteria use it?

salt causes cells to shrink because the water rushes out of cells to restore equilibrium to adapt, cells will bind water and keep it inside the cell without interfering with cellular processes

how are viruses typically grown in the lab?

several schemes for growing viruses in lab are common: (1) embryonated chicken eggs (flu, others) (2) bacteria (bacteriophage) (3) tissue culture (many animal viruses) (4) plants or plant tissue culture

If you had a bacterial cell in a solution of sodium at 0.5 M outside the cell and 0.8 M inside the cell, and K+ at 0.3 M outside the cell and 0.5 M inside the cell. If this is an anti-porter, with the sodium coming into the cell as the potassium (K+) leaves the cell, which molecule, sodium or potassium, provides the energy for this transporter? How do you know?

sodium is going from 0.5 M outside the cell to 0.8 M inside the cell (low > high). potassium is going from 0.5 M inside the cell to 0.3 M outside the cell (high > low). therefore, *potassium* provides the energy for this transporter because it is moving from inside the cell to outside of it (moving WITH its gradient). the sodium is moving against its gradient.

can unspoiled food be unsafe to eat? can spoiled food be safe to eat? defend.

some spoiled food can actually be eaten safely. an example would be cottage cheese or sauerkraut. conversely, some unspoiled foods can be unsafe to eat, such as raw chicken or raw eggs.

why is tamiflu only given in the early days of influenza infection?

tamiflu inhibits the shedding stage of the virus, so it prevents more cells from being infected. if almost all the cells are already infected, this does not have much of an impact. antimicrobials act on unique features such as 70S ribosomes or peptidoglycan. antivirals tend to target unique viral enzymes and processes. there are not a lot of these that do not harm the host. Tamiflu, reverse transcriptase (RT) and protease inhibitors, and ribavirin are best to use.

why is the proofreading activity of the RNA-dependent RNA polymerase of SARS-CoV2 important to public health and vaccine development?

the RNA-dependent RNA polymerase has a proofreading capacity. this is important because it has a lower mutation rate than a virus that does not include proofreading enzymes.

what determines the arrangement of bacterial cells?

the arrangement of bacterial cells is determined by a protein called MreB. MreB forms a spiral bond - a simple cytoskeleton - around the interior of the cell, just under the cytoplasmic membrane. it is thought to define shape by recruiting additional proteins that then direct specific patterns of bacterial growth.

would a microscope with a resolution of 25 µm be better or worse than a microscope with a resolution of 5 µm?

the better the resolution (greater the number), the better the microscope. so, we would choose the *25 µm microscope* over the 5. higher magnification (40X, 100X) is better for close-ups and detailed work, while lower magnification (4X, 10X) is better for a larger field of view.

compare and contrast the growth curve seen when measuring the growth of viruses (burst size) and that of bacterial cells (binary fission). calculate the number of bacteria present after 4 generations when starting with an initial concentration of 100 CFU/mL.

the curve with binary fission has an exponential curve, growing and dividing by two. viruses divide at a MUCH higher rate, therefore the graph for a virus will be much steeper. 100*100*100*100 = 100,000,000

would the loss of cro protein prevent prophage formation or prevent induction? why?

the loss of cro protein would prevent induction, since the formation of prophages is an objective of cro protein

Diagram how the use of antibiotics leads to resistant populations.

the more an antibiotic is used, the more resistant a population becomes to it (selective pressure). *Selective pressure*, or evolutionary pressure, defines the causes that reduce reproductive successes in a portion of a population that drives natural selection.

When a physician doesn't know the cause of a disease (e.g. pneumonia has the same symptoms but multiple causes), would he or she prescribe a narrow or broad-spectrum drug? What other variables do they need to consider?

the physician would prescribe a broad-spectrum drug, because broad-spectrum drugs target many things that could help reduce symptoms and remove the disease. other variables that need to be considered include side effects, symptoms, other medication being taken, etc.

how can E. coli take 40 minutes to duplicated its DNA, but have a generation time of 20 minutes? why does this seem like a paradox?

there can be multiple origins of replication at the same time in the bacterial cell. as DNA is replicated at one point to form a new strand, DNA is being replicated from that new strand that forms a second new strand. when the cell divides, part of the daughter cell's DNA has already been replicated.

what conditions favor lytic phage and which favor temperate phage? why is stress to the cel las a trigger to induction evolutionarily favorable?

there is no "best" way. it depends a lot on the virus, its host, and the relative concentration of host cells to viruses. when hosts are plentiful, the lytic is favored. when hosts are harder to find, lysogeny is favored. phage need to produce late genes to make their virions to then infect new cells, stressed cells may die before this happens. RecA levels rising leads to stress, triggering induction, so the phage can make new virions and leave before the cell dies.

is there a vaccine or other preventative measures available to limit the spread of HIV? explain.

there is no vaccine for AIDS, but PrEP (pre-exposure prophylaxis) can be taken as a precautionary measure too bind the reverse transcriptase inhibitors, thus inhibiting the likelihood of infection.

what was the first virus discovered? how was it discovered? what does the term "virus" mean?

tobacco mosaic virus (TMV) was the first virus discovered. it is an RNA virus that infects tobacco and tomatoes. "virus" indicates an infectious agent that causes disease

why does an electron microscope have a much better resolution than a light microscope? how does a TEM differ from a SE<?

transmission electron microscopes (*TEM*) provide details on internal structures, while scanning electron microscopes (*SEM*) provide fine details of exterior structures. electron microscopes use beams of electrons, not light, and their samples are stained with heavy metals (e.g., gold or uranium salts). they increase resolution by decreasing wavelength; the smaller the wavelength, the lower the value of "d" (resolution), so closer distances can be seen via better resolution and higher magnification.

Can the viable cell count ever be higher than the total cell count? Why or why not?

viable count can never be higher than the total cell count.

what is the relationship between viruses and vaccines? what is the current recommendation for polio and smallpox vaccination in the US?

viral diseases led to the development of some of the first vaccines. there are different types of vaccines and each type has different advantages. attenuated vaccines are more effective and can "vaccinate" someone without actually giving a shot. other people expel the virus and can transmit it through feces and other ways to people who are not vaccinated.

compare and contrast plant and animal viral infection.

viruses that infect plants are transmitted by an insect vector because cell walls are a barrier to infection. viruses can then go from cell to cell via channels within the plant. viruses that infect animals do not have to penetrate a cell wall to enter the cell.

Why do bacteria grow faster as the environmental temperature increases, but then stop growing as the temperature exceeds the maximum temperature?

warmer temperature means that molecules will move faster. too hot of temperatures, however, will cause proteins to denature (thermal lysis).

why do we stain samples?

we stain samples to see them better through a microscope. without staining, certain features of the cells (cell walls, for example) can be unclear and lead to incorrect interpretation of microbes.

which bacteria are positive when stained with an acid-fast stain? how does a negative stain enable researchers to see structures? which structure(s) are seen with a negative stain?

we use acid-fast stains for mycobacteria since they have a waxy coat that doesn't stain well during gram-stains. the mycobacteria serve as our positive bacteria. negative stains are the background being stained, not the bacteria, which allows us to see and identify structures. we can see structures such as endospores and flagella through this process.

Given that penicillin inhibits the formation of new cell walls, would you categorize it as bacteriostatic, bacteriolytic or bactericidal?

you would categorize penicillin as bactericidal; penicillin works by inhibiting bacterial cell wall synthesis. not being able to form new cell walls is when a bacterial cell dies.