Microbiology Final Exam 3 (Viruses and Fungi)

What antimicrobial targets DNA and RNA synthesis?

(cipro, rifampin)

Heat affects...

1) proteins (enzymes) 2) nucleic acids (DNA and RNA structure) 3) other small molecules

What specific medium must be used in testing the effectiveness of antimicrobial drugs?

Mueller-Hinton medium

Which statement describes the difference between the normal neuron protein PrPC and the pathogenic version PrPSc?

The amino acid sequence is identical, but the three-dimensional conformation is different.

What is the importance of inoculating a control plate in lethal temperature experiments?

The control plate with bacteria not exposed to high temperatures is used for comparison and to ensure that the bacteria are capable of growth

If an infectious agent is sensitive to several antimicrobial drugs, what other considerations might be used to determine the best treatment option?

Therapeutic index of the agent, cost, other patient health issues, allergies, etc.

Which of the following examples is an example of lysogenic conversion?

Vibrio cholerae bacteria produce cholera toxin when infected with a phage.

• Oligotroph:

____________________ an organism that grows best at very low nutrient concentrations

Antibiotics are produced by __________________ as a defense mechanism against other organisms.

bacteria and fungi

Viruses rely on the_______________ to make new viruses, but they sometimes provide their own ___________ (such as reverse transcriptase, which is an RNA-dependent DNA polymerase).

host cell machinery, enzymes

• Soil can be divided into two broad groups:

mineral and organic

Leishmaniasis is transmitted by which of the following vectors?

sandflies

Thermal death time

the shortest time required to kill a suspension of cells or spores under defined conditions at a given temperature

Treating milk at 150 degrees for 1-3 seconds to control microbial populations is called:

ultra high temperature pasteurization

A living organism that transmits diseases is called a _______________.

vector

_________________ is essentially an in vivo fermentation vessel, with the microbiota using nutrients derived from the digestion of food.•

• The colon

________________ derived from rock weathering and other inorganic materials

• mineral soils

Transcription in a virus that has an RNA genome is more complex than in a DNA-based virus because __________.

1) the virus must make an RNA complement from its RNA genome, and the host cell does not have the machinery for this process 2) the virus must carry its own RNA-dependent RNA polymerase 3) the viral genome must encode for RNA-dependent RNA polymerase

____________ precede DNA viruses, lead to three domain of cellular life.

RNA viruses

Which of the following fungal genera causes athlete's foot?

Trichophyton

bacteriocidal

agents that kill bacterial cells

Reverse transcriptase is:

an RNA-dependent DNA polymerase

The lytic cycle of a temperate virus would probably be induced by_______________.

damage to the cell's DNA

A unique spore photo-product is generated by UV light in endospores that functions in _____________________ during endospore germination.

enzymatic repair of damaged DNA

Fungi are __________.

hemoorganotrophs

Alexander Fleming

noticed that Penicillium, a fungus, inhibited growth of the bacterium, Staphylococcus aureus when both organisms were present on the same agar plate

The capsule surrounding bacterial cells is mostly composed of ____________________.

polysaccharides

Herpesviruses can cause __________.

shingles, cold sores or fever blisters, cancer

The DNA of endospores is protected by ____________ that bind to DNA and alter its conformation, thereby protecting it from photochemical damage from UV light.

small acid-soluble proteins

Thermal death point

the lowest temperature at which a population of the target organism is killed in 10 minutes

What factors influence the size of the zone of inhibition produced by a chemical?

the molecular weight of the agent and its rate of diffusion in the agar.

What antimicrobial targets cell wall synthesis?

(penicillin)

To measure the culture temperature, why is the thermometer placed in a tube separate from the culture?

If the thermometer was in a culture tube it would interfere with the subsequent transfers of culture to plates across the time intervals and be a source of contamination

Ultraviolet (UV) Light

Non-ionizing short-wavelength radiation that falls between 4nm and 400nm in the visible spectrum; more germicidal than either visible light or infrared radiation.

Antibiotics

are natural compounds produced by microbes

When determining the number of virus particles in a suspension, why is the number obtained always less than the actual viral titer?

because all of the virus particles do not infect with 100% efficiency

Which of the following treatment would not remove or kill the Giardia parasite in water?

chlorination

Pyrimidine dimers

covalent bond between two adjacent thymine or cytosine molecules in a DNA strand; caused by absorption of UV light

Antimicrobials

drugs that are partially or entirely synthesized in a lab

What is the most common sign of infection by Toxoplasmosis?

no sign, since most infections are asymptomatic

What antimicrobial targets vitamin synthesis?

(sulfa drugs)

What antimicrobial targets protein synthesis?

(tetracyclines, streptomycin)

Modes of action for antimicrobials?

1) Affects whether an antimicrobial is narrow or broad 2) Permeability also affects function (harder to penetrate gram-negative cells

Antibiotic resistant strains

1) Staphylococcus aureus 2) Pseudomonas aeruginosa 3) Mycobacterium tuberculosis 4) Neisseria gonorrhoeae 5) Enterococcus

How are viruses different from living organisms?

1) Viruses are acellular and all living things are made up of cells 2) Viruses have DNA or RNA, not both 3) Viruses depend on their host to synthesize the essential components of new viruses (e.g., genetic material and proteins), while living organisms are capable of synthesizing these components even if they require a host for food, shelter, or other necessities.

List four diseases caused by spore-forming bacteria

1) anthrax 2) tetanus 3) botulism 4) gas gangrene (aka myonecrosis)

What factors influence the size of the zone of inhibition for a particular antimicrobial?

1) diffusibility of the agent 2) size of the inoculum 3) type of medium 4) resistance mechanisms of the test organism

Give three reasons why endospores are much more resistant to heat than are vegetative cells,

1) tough spore coat 2) low moisture content 3) large amount of calcium and dipicolinic acid

Broad-spectrum antimicrobials

Effective against both gram- positive and negative organisms, Ex. ciproflaxin

How might the physical differences between gram-positive and gram-negative bacteria contribute to differences in chemical resistances?

Gram-negative bacteria have outer membranes that may limit penetration of chemicals that harm cytoplasmic targets

Why are gram-positive bacteria typically more resistant than gram-negative bacteria to antimicrobials that disrupt plasma membranes, such as polymyxin B?

Gram-positive bacteria have thick cell walls that maintain cell stability even when the plasma membrane is disrupted by polymyxin B

Bacillus megaterium has a high thermal death point and a long thermal death time, but is not classified as a thermophile. Why?

It is a mesophile and in its vegetative state it would be killed at high temperatures. The endospores it produces, however, are extremely heat resistant (thermoduric) and allow the bacteria to survive until plating and incubation at an optimal temperature

What type of agar is recommended for the Kirby-Bauer method?

Mueller-Hinton II agar is the recommended medium with pH between 7.2 and 7.4

Are viruses that infect Archaea different from bacterial viruses?

No; they consist of nucleic acid and protein like other bacterial viruses.

Which of the following types of enzymes would a virus need to provide in order to replicate within a cell? In other words, which of these enzymes would not normally be found in a cell unless a virus provided it?

RNA replicases (RNA-dependent RNA polymerases) for RNA viruses

A fungus that is coenocytic, is involved in food spoilage, and produces asexual spores in a sac could be __________.

Rhizopus

Narrow-spectrum antimicrobials

Specific in target; Targets gram-positive or gram-negative, Ex. penicillin

Why are certain gram-negative bacteria more resistant than gram-positive bacteria to antimicrobials that attack cytoplasmic targets?

The outer membrane of gram-negative bacteria acts as a permeability barrier and can restrict the entry of antimicrobials into the cell

Would heating the culture in a sealed, small-diameter tube that is totally immersed in a water bath produce more accurate results than the use of tubes that are partially submerged in a water bath?

Using totally immersed tubes is preferable because samples would be uniformly exposed to the prescribed temperature. In partially immersed tubes, a temperature gradient can occur between the portion of the tube immersed in the water bath and tube portion above the water level.

sanitizers

agents that reduce microbial numbers to a safe level but do not completely eliminate all microbes

Semi-synthetics:

antimicrobials that are chemically synthesized in the laboratory and are not produced by microbial biosynthesis at all; ex. sulfa drugs

Antibiotics:

antimicrobials; usually of low molecular weight, naturally produced by microorganisms to inhibit or kill other microorganisms; ex. penicillin and streptomycin

Control of microorganisms on living tissue using mild chemical treatments is called__________.

antisepsis

Antimicrobials:

any compounds that kill or inhibit microorganisms

disinfectants

chemical agents that are applied to inanimate objects such as floors, walls, and tabletops to kill microorganisms; damaging to living tissue

Naked viruses such as the Rhinovirus can penetrate animal cells by_______________.

creating a pore in the host membrane

Superficial mycoses are caused by a group of fungal pathogens called __________.

dermatophytes

sterilants; sporocides

destroy all microbial life, including endospores; ex. ethylene oxide

SOS system

enzymatically removes the dimers and inserts in their place new pyrimidine molecules.

Disinfectants

examples: bleach, Lysol, ammonia; are used on inert surfaces (e.g., tabletops); most are not recommended for use on skin, are used on surfaces to kill microorganisms but not necessarily endospores.

Which of the following would be adequately sterilized by UV radiation alone?

exposed surfaces only

Healthcare acquired infections (HAIs)

formerly nosocomial infections; acquired in hospitals; MRSA is responsible for many hospital infections

Most viral genes from nature have no existing ____________ , so much of their genomes will be new to biology.

homologs (shared ancestry)

The fungal mycelium is made of up individual strands that are each called__________.

hypha

bacteriostatic

if a particular agent only inhibits the growth of bacterial cells but does not kill them

If bacterial isolate shows intermediate to moderate resistance to an antimicrobial, how might this drug still be successfully used in the treatment of this microbe?

increasing the dosage of the antibiotic may effectively counteract the resistance and successfully treat the infection

Aminoglycoside antibiotics such as Streptomycin have which mode of action?

interfere with protein synthesis

Why does penicillin have selective toxicity against bacteria but not humans?

it interferes with peptidoglycan sythesis

Coccidioidomycosis (a mammalian fungal disease) most commonly causes which of the following types of diseases?

it is a common cause of community-acquired pneumonia in the endemic areas of the United States. Infections usually occur due to inhalation of the arthroconidial spores after soil disruption. The disease is not contagious. In some cases the infection may recur or become chronic.

Most organisms are restricted to the ______________ of the large intestine, while others are in the _________________________.

lumen, mucosal layers

Viral structural proteins and proteins involved in the release of new viral particles that are synthesized after genomic replication begins would be considered __________.

middle and late proteins

Malaria could be caused by which of the following organisms?

mosquitoes

What is the term used for the filamentous body found in many fungal species?

mycelium

A prion is an infectious particle having a protein component and _________________.

no nucleic acid

Only a few groups of viruses can be reliably traced in phylogenies, an example would be:

nucleocytoplasmic large DNA viruses (NCLDV): Mimivirus and relatives

Viral phylogeny -- Universal phylogenetic tree constructed from combination of:

protein sequences and structural features.

• Pelagibacter and other marine heterotrophs contain ______________________ , a form of rhodopsin that allows cells to use light energy to drive ATP synthesis.

proteorhodopsin

Which virus was the first viral vaccine developed for?

smallpox

What structure can the viral genome take?

ss-DNA ds-DNA ds-RNA

antiseptics

substances such as alcohol or betadine that inhibit microbial growth or kill microorganisms but they are gentle enough to be applied to living tissue; do not destroy endospores

Which of the following classes of antimicrobial drugs interferes with folic acid synthesis in bacteria?

sulfa drugs

Which of the antibiotic targets listed would be LEAST useful in a clinical setting due to possible toxicity?

the DNA major groove

UV radiation at 260 nm

the MOST germicidal, because it the wavelength at which DNA maximally absorbs UV light

Where is Histoplasmois most commonly found within the United States?

the Mississippi valley and along the border between Texas and Mexico

zone of inhibition

the area around the disk where no growth occurs if an agent inhibits the microorganism; affected by diffusibility of the agent, size of the inoculum, the type of medium, and other factors

Kirby-Bauer method

used to determine the sensitivity or resistance of a bacterium to an antimicrobial; performed by streaking a standardized inoculum of the test organism on Mueller-Hinton medium, and then paper disks containing specific concentrations of an antimicrobial are deposited on the agar surface. The antimicrobial diffuses out from the disk into the agar, forming a concentration gradient. If the agent inhibits or kills the test organism, there will be a zone around the disk where no growth occurs, called the zone of inhibition.

How does Histoplasma capsulatum get dispersed throughout the body?

within macrophages

Other Visceral Parasites: • Trichomonas vaginalis

• flagellated anaerobic parasite • has hydrogenosomes • transmitted person-to-person by sexual intercourse • can survive on moist surfaces • can be transmitted by toilet seats, sauna benches, and towels • asymptomatic in males • vaginal discharge, itching, and burning in women • antiprotozoal drug metronidazole used in treatment

___________________ derived from sedimentation in bogs and marshes

• organic soils

• Soil

• the loose outer material of Earth's surface; consists of four distinct layers.