MCRO lab exercises 16-23
2 kinds of indicator bacteria used for these experiments:
Test: MPN, LST-MUG - detects fecal coliforms (presumptive test for E. coli) Test: N/A, EMB - detects E. coli (confirmation test for E. coli) Test: MF, KF-strep agar - enterococcus species and fecal streptococcus species.
bacillus species
produce polymyxins and bacitracin
common denitrifies
- pseudomonas, bacillus, clostridium
pseudomonas denitrification
complete denitrification to nitrogen gas
how much stuff do you add to each well ammonium?
- 100 microliters OPA reagent - 50 microliters peptone broth - 50 microliters TCA
If dilutions 10^-8, 10^-7, 10^-6, yield avg 30, 280, 568 colonies, what is the PFU/ml of the phage solution tested?
- 280 and 568 are greater than 250 TNTC. - 30/(10^-8)(1ml volume plated)=3e9
Indicator bacteria
- Characteristics: used to determine the sanitary quality of water. - present when fecal pathogens are present - found in all types of water:M hot tubs, rivers, lakes, oceans. - longer survival time than the hardiest enteric pathogens (gastrointestinal tract) - found in the intestines of warm-blooded mammals.
Determine CFU/ml
- Count how many colonies - if there are 20 colonies, then 20 CFU/100ml as 100 ml of water was filtered
Mannitol salts agar
- Differential and selective for staphylococcus species while some micrococcus species may also grow. - Selective: high NaCl content of 7.5%: many organisms are inhibited except for those that are halo tolerant - differential: mannitol acidifiers such as S. Aureus show yellow zones around their colonies due to acid production and subsequent changes in the phenol red pH indicator from mannitol fermentation. - s. Epidermidis does not ferment mannitol and remains red.
Mitis Salivarius Agar
- Differential and selective for streptococcus species. - Tellurite (selective and differential) - selective: inhibits all gram negative, most gram positive and molds - differential: reduced by enterococci (black colonies) - crystal violet (selective) - selective: inhibits gram positive - tellurite and crystal violet should inhibit growth of all bacteria except streptococcus and enterococcus. - Trypan Blue dye (differential) - absorbed by streptococci (blue colonies) - s. mitis, s. salivarius, s mutans - Sucrose (differential) - metabolism (large and mucoid/sticky colonies) - +: s. mutans and s salivarius - -: enterococcus and s mitis.
What are standards for coliforms in drinking water? Who establishes these standards?
- EPA - MPN test is statistical measure - coliforms: <2.2MPN/100 ml - fecal coliforms: zero tolerance - MF test is direct count - enterococcus/fecal streptococcus <1 CFU/100ml
EMB agar
- Eosin Methylene Blue Agar (EMB) - This agar medium is both selective and differential. The combination of the two dyes eosin and methylene blue inhibits most Gram positive bacteria but allows many Gram negative organisms to grow. (both selective) - In addition to peptones, EMB contains lactose (it may also contain sucrose). Gram negative bacteria that ferment the lactose produce acid which turns the colonies dark purple as the acid acts upon the dyes. (differential) - In addition, certain lactose-fermenting bacteria produce flat, dark colonies with a green metallic sheen. Other lactose fermenters produce larger, mucoid colonies, often purple only in their center. Lactose non-fermenters are either colorless or light lavender.
GUD
- GUD, which cleaves the 4-methylumbelliferyl-beta-D-glucuronide (MUG) substrate to release (MU) - when exposed to long wave UV light (365 nm), MU exhibits a bluish fluorescence.
Common skin bacteria
- Gram positive: staphylococcus, bacillus, streptococcus, and propionibacterium - propionibacterium is associated with acne vulgaris
Blue colonies
- Indicate that sucrose is fermented by the organism
LST-MUG broth
- Lauryl Sulfate Tryptose: selective. selects against gram positive bacteria, promoted growth of gram negative bacteria. - Lactose: differential. lactose fermentation. positive for gas indicates a coliform. - 4-methyllumbelliferyl-ß-glucoronidase (MUG): differential. Bacteria with the enzyme GUD can break down. positive for fluorescence indicates fecal coliform.
Skin environments
- Little moisture, acidic pH, high salt concentration. - sweat glands release lysozyme, which attacks the cell wall of gram positive bacteria and antimicrobial peptides called cathelicidins
Determine MPN index, what does the MPN index number represent?
- MPN index: look at table - used to determine the most probable number of fecal coliforms in a sample.
Use EPA standards for potable water
- MPN test is statistical measure - coliforms: <2.2MPN/100 ml - fecal coliforms: zero tolerance - MF test is direct count - enterococcus/fecal streptococcus <1 CFU/100ml
What is the difference between the MPN test and MF test
- MPN test is statistical measure - coliforms: <2.2MPN/100 ml - fecal coliforms: zero tolerance - MF test is direct count - enterococcus/fecal streptococcus <1 CFU/100ml
How might diet reduce the incidence of cavities?
- Milk, cheese and yoghurt contain minerals such as calcium, casein and phosphorus that help protect tooth enamel. Casein is a protein found in dairy foods. When combined with calcium and phosphorus, casein creates a protective protein film over the enamel surface of the tooth, reducing the risk of tooth decay. - bacteria in the mouth metabolize fermentable carbohydrates from our diet most notably sucrose and other things found in high sugary foods and substances.
Plate count agar
- PCA is a general purpose medium that supports the growth of many bacteria (aerobic heterotrophs, then heated for endospores)
Most of these skin bacteria colonize?
- Regions surrounding oil and sweat glands and hair follicles. - glandular secretions provide a source of nutrients for the bacteria. - halotolerant bacteria are able to survive high salt concentrations
How do we observe the T4 bacteriophage in this experiment?
- T4 bacteriophage is observed via plaques. as it undergoes the lytic cycle to infect E. coli cells and kill them to create plaques.
organisms that cause disorder affecting the skin, eye, ear, throat, and CNS transmitted through water
- Viruses: hepatitis A, hepatitis E., and poliovirus. - skin irritations: staphylococcus aureus, pseudomonas aeruginosa, leptospina, shistosoma species. - CNS: the protozoan Naegleria Fowleri causes primary amoebic meningoencephalitis (PAM) from lakes or pools.
What bacterial structure would you expect bacteria that live on the surface of your teeth and gums to have?
- a capsule or slime layer that enables them to stick to your teeth. - virulence factor look at for streptococcus mutans.
How might you isolate a free-living nitrogen fixer like azotobacter from the soil?
- add soil to nitrogen free broth medium with mannitol for energy and carbon sources
broad spectrum antibiotics
- affect a broad range of gram-positive or gram-negative bacteria - used t routinely treat bacterial infections -
nitrogen containing compounds
- amino acids - ATP - nucleic acids - chlorophyll
Why is good dental hygiene important for disease prevention?
- bacteria reach levels where cause tooth decay and gum disease. streptococcus mutans poops out acid that affects the enamel on teeth and wears it down create a hole called a cavity.
Why is skin a poor growth environment for microbes?
- because little moisture, nutrients are limited, high salt concentration, and slightly acidic.
Calculate PFU/ml
- between 30 and 300 plaques. - average number of plaques/ (volume plated) (dilution of the tube)
Streptomycin
- broad spectrum - bactericidal - mode of action:causes frame shift mutations-->production of faulty proteins - cell death
Ampicillin
- broad spectrum - bactericidal - mode of action: inhibits transpeptidase--> cell wall weakens. enzyme responsible for cross-linking./ - cell death
Tetracycline
- broad spectrum - bacteriostatic - mode of action: ceases protein synthesis - cells can exist on pre-existing proteins but can't grow
gram of soil
- can contain 10^8 or 10^9 cells. - members are fungi (penicillium or aspergillus), actinomycetes ("branching bacteria such as streptomyces). and other bacteria (bacillus, clostridium, pseudomonas).
what clinical relevance does antibiotic sensitivity testing have?
- can track how antibiotic resistance is developing within strains of bacteria. - some antibiotics may no longer effective in treating some bacterial infections. - An antibiotic sensitivity test can help find out which antibiotic will be most effective in treating your infection. The test can also be helpful in finding a treatment for antibiotic-resistant infections.
fecal contamination
- causes potable water to become contaminated. microbes of fecal origin cause water-borne disease outbreaks, such as shigella species sand salmonella species.
what are problems regarding the extensive use of antibacterial compounds in soaps, disinfectants, cutting boards, and toothpaste?
- causes the bacteria exposed to these antibacterial environments to undergo an environment in which natural selection can take place. - natural selection selects for bacteria that are resistant to these compounds. Get bacteria that have antibacterial resistance. Evolutionary arms race.
ETEC (enterotoxigenic E. coli)
- causes travelers diarrhea. - produce one or two enterotoxins, which result in the hypersecretion of electrolytes and water into the intestinal lumen.
disinfectants and antiseptics
- chemically control microbes in our environment - phenolics, alcohols, halogens, and quaternary ammonium compounds. -modes of action: denaturation of proteins, disruption of membranes, and oxidation of cellular constituents. - quaternary ammonium compounds are effective against most bacteria but are ineffective against mycobacterium and endospores.
LST-MUG test
- combines the classic presumptive test for coliforms (gas production in Lauryl tryptose broth) with a fluorescent test for the enzyme beta-glucuronidase (GUD) which indicates E. coli (a notable example of a fecal coliform). - 94% of E. coli strains produce GUD, which cleaves the 4-methylumbelliferyl-beta-D-glucuronide (MUG) substrate to release (MU) - growth: gram negative, growth and gas: coliform, growth gas and fluorescence: fecal coliform.
denitrification
- converts nitrate to nitrite - converts nitrite to N2, which is an unusable form of nitrogen -can have partial to complete denitrification
accurate results for Kirby Bauer
- dependent on innocuous size, innocuous distribution, incubation period, depth of agar, growth rate of bacteria, and the diffusion rate of of the antibiotic through the agar.
Hemolytic types
- differentiated using blood agar. - alpha hemolytic: becateria produce a zone of green l, olive, or brown discoloration around their colonies due to the oxidative effects of peroxide on heme. (The pigmented portion of hemoglobin), turning the hemoglobin to methehemoglobin. A large group of streptococcal bacteria are in this group. partial break down - beta hemolytic: produce a zone of clearing around their colonies (complete hemolysis), due to lysis of erythrocyte membranes and cell destruction by the production of toxins called hemolysins. The presence of beta hemolytic bacteria indicates a pathogenic organism such as the causative agent of strep throat (streptococcus pyogenes). complete break down -gamma hemolytic: such as enterococcus, will exhibit no detectable change in blood agar around their colonies. no break down
Narrow spectrum antibiotics
- effective for narrow group of bacteria either gram positive or gram negative - penicillin inhibits cell wall synthesis and is mainly effective agianst gram positive bacteria only.
Sabouraud's agar
- encourages the growth of fungi due to a slightly acidic pH (~5-6) and high sugar content - penicillin and streptomycin are also added to this SAB agar to further inhibit the growth of bacteria.
Indicator bacteria for fecal contamination
- enterococci - gram positive - facultative anaerobes - survives at high salt concentrations best indicator for saltwater, but also can be used for freshwater) - host-specific: cattle, sheep, and other ruminants: enterococcus bonus and equinas. humans: e faecelis.
nitrogen fixers.
- free-living: azotobacter and cyanobacterium - symbionts: Bradyrhizobium and rhizobium form symbiotic relationships with legumes, while Frankia forms symbiotic associations with woody shrubs - carry out the reaction of fixing nitrogen gas into usable forms by the enzyme nitrogenase.
define coliforms, are all coliforms from the fecal origin?
- gram negative, non-sporulating, facultative rods that ferment lactose with the production of gas within 48 hrs. - no, many are just commensals of the intestines of warm blooded animals.
enterococcus
- gram positive - GI tract - catalase negative - commensals: e faecalis, E faecium
streptococcus
- gram positive - mouth, nasal passage, GI tract, Pharynx - catalase negative - commensals: s. mitis and s. salivarius opportunistics: s. mutans, s. pneumoniae, and s pyogenes.
staphylococcus
- gram positive - skin and nasal cavity - catalase positive - major cause of nosocomial infection - commensal: s epidermidis - opportunistic: s aureus (staph infection)
bacillus and clostridium
- gram positive bacteria that are able to form endospores. - endospores are dormant form of the bacterial cell that are able to survive harsh temperatures such as high temperatures, desiccation, radiation, and low nutrients.
LST-MUG
- growth vs no growth: growth, promising but need gas also to be a positive result for LST-MUG test - gas in Durham tube vs no gas in Durham tube: characteristic of a coliform is that it ferments lactose to gas within 48 hrs. - fluorescence vs no fluorescence: strong fluorescence indicates the presence of e. Coli as 94% of E. Coli have GUD enzyme which cleaves MUG to MU. MU reacts with long wave UV light (365 nm) when exposed. Must be same amount of fluorescence as the E. Coli control
MF test
- is a direct count unlike the MPN test - CFU/ml -<1 CFU/100ml is EPA standard
symbiotic relationship between bacteria and plant
- is very specific, which certain biovars of bacteria that only colonize one type of plant (for example, clover) - symbiotic bacteria live within root nodules. interior of root nodules is kept free of oxygen since nitrogenase enzyme is extremely sensitive to oxygen.
Lytic vs lysogenic cycle
- lytic cycle: 1. Viral particle attaches to the host cell by attaching to specific host receptor 2. genome penetration occurs. T4 viral particle injects its DNA genome from the capsid into the host cell cytoplasm. 3. synthesis of new viral proteins and nucleic acids occurs. 4. these components are made from host cell polymerases, ribosomes, monomers, and use ATP provided by the host cell. Then they are assembled into viral particles. 5. new viral particles are released via cell lysis. The lytic cycle involves the reproduction of viruses using a host cell to manufacture more viruses; the viruses then burst out of the cell. - The lysogenic cycle involves the incorporation of the viral genome into the host cell genome, infecting it from within.
microbe role in soil ecosystem
- microbes play an important role in soil ecosystems including decomposition of organic matter and nutrient cycling.
What are some skin diseases that might be cause by members of the normal micro flora?
- most skin bacteria are commensals, but if they enter a wound they may become opportunistic pathogens. If normal skin commensals enter the bloodstream they ma use septicemia.
Penicillin
- narrow spectrum - bactericidal - mode of action: inhibits transpeptidase--> cell wall weakens - cell death
nitrate reduction experimental set-up
- nitrate broth - inoculated with bacteria and incubated with Durham tube.
name the bacterial genera involved in nitrification. what about denitrification?
- nitrification: notrosomonas and nitrobacter - denitrification: bacillus, clostiridium, pseudomonas
What are the main steps of the nitrogen cycle? Which steps are beneficial to soil fertility and which steps are detrimental?
- nitrogen fixation, nitrification, denitrification, ammonification, assimilation - denitrification is only one that is detrimental
if no bubbles after the addition of sulfamic acid, add what?
- no bubbles indicates nitrate was reduced to a form of nitrogen that we are not testing for such as ammonia orrr - nitrate was not reduced - add zinc dust to the test tube and observe. prolonged intense fizzing after the addition of zinc dust indicates a negative result for nitrate reduction. - zinc dust reduces nitrate to nitrite, which will be reduced to nitrogen gas by the sulfamic acid already present in the solution.
consider the statement bacillus anthracis demonstrates a zone of inhibition of 15mm for both penicillin G and streptomycin, does this mean it is equally sensitive to both antibiotics? can either be used to treat a disease caused by this pathogen?
- no, because antibiotic a might diffuse faster through the agar than antibiotic b. Not equally sensitive to both. - no not necessarily, each drug- bacteria pair has its one susceptibility/ resistance range its possible they both work equally and could be used to treat a pathogen but not for suresometimes a zone as large as 28mm can still be considered resistant, and sometimes a zone a small as 11mm would be considered susceptible
Blood Agar Plate (BAP)
- nutrient (enriched) and differential media used to identify Streptococcus bacteria which produce exotoxins that lyse red blood cells - cultivation of nutritionally fastidious organisms, such as streptococcus species - not selective
nitrogen fixation
- process of converting nitrogen gas into nitrogen compounds that plants can absorb and use. - diazotrophs are able to do this - rhizobium, azobacter, cyanobacteria are kinds of these
nitrogen fixation
- process of converting nitrogen gas into the amino form, NH2, that can then be incorporated into organic molecules. - unavailable nitrogen becomes biologically available through this process.
species of the bacterial genus streptomyces
- producers of streptomycin, chloramphenicol, erythromycin, neomycin, rifampicin, and tetracycline
KF strep agar
- selective for streptococcus and enterococcus due to addition of sodium azide, which inhibits growth of organisms that have a strict respiratory metabolism -TTC in agar makes in differential, colonies of appear deep red to pink. tetrazolium salt, which is reduced by viable cells (metabolically active) to form insoluble formazan (red) inside the bacterial cell. TTC is also slightly inhibiting the growth of other organisms. - can only occur under a low oxygen environment like a candle jar.
KF-strep
- selective for streptococcus and enterococcus species Due to the addition of sodium azide, which inhibits the growth of organisms that have a strictly respiratory metabolism (ETC). - enterococci appear deep red due to the addition of 1% sodium azide, which is a tetrazolium salt
anaerobic soils
- some bacteria carry out anaerobic respiration using nitrate as the terminal electron acceptor - reduces nitrate to nitrite or nitrogen gas and results in a biological loss of available nitrogen
groundwater
- source of excess nitrogen (fertilizers NO3-) - negative impacts: algal blooms, methemoglobinemia
wastewater
- source of excess nitrogen: sewage NH3/NH4 - negative impacts: algal blooms - expensive to go through nitrification and then denitrification - cheaper to go through annamox
other indicators than E. coli in water
- streptococcus mitis-slaivarus, pseudomonas aeruginosa indicators of possible skin, eye, ear, or throat infections.
Microorganisms taht colonize the throat
- streptococcus, staphylococcus, corynebacterium, neisseria, and haemophilus - pathogenic: streptococcus pneumoniae and haemophilus influenzae and neisseria meningitidis.
If bubbles form after addition of sulfamic acid
- sulfamic acid is able to reduce any nitrite present to nitrogen gas and fizzing occurs. - indicates nitrate was reduced to nitrite via a nitrate reductase, so undergoes partial denitrification.
why is 4% peptone broth a suitable medium to detect ammonification?
- the peptone broth contains a mix of partially hydrolyzed proteins and serves as a source of organic nitrogen to use
how are serial dilutions performed?
- through the addition of 1 ml of the previous solution to a new dilution blank containing 9ml for a total of 10 ml.
Coliform and fecal coliform characteristics
- used as indicator organisms to determine sanitary quality of water because hard to test for each pathogen individually - easy to detect COLIFORMS - gram - - non sporulating - facultative rods - that ferment lactose with the production of gas at 35ºC FECAL COLIFORMS - common commensals of intestines of warm blooded animals - fecal = E.coli - lactose fermentationL gas and acid production at 42ºC - not all are fecal, some soil.
fecal coliform bacteria
- used as indicator organisms to determine sanitary quality of water because hard to test for each pathogen individually - easy to detect COLIFORMS - gram - - non sporulating - facultative rods - that ferment lactose with the production of gas at 35ºC FECAL COLIFORMS - common commensals of intestines of warm blooded animals - fecal = E.coli - lactose fermentationL gas and acid production at 42ºC - not all are fecal, some soil.
MPN test
- used to determine the most probable number of organisms, usually coliform, present in a sample. - It is a statistical estimate and not a direct count. - 10ml of water sample added to each of the 5 broth solutions. - 2.2 MPN/100ml
Did your blood agar plate indicate the potential presence of a pathogenic strain?
- yes, beta-hemolytic bacteria is pathogenic - streptococcus pyogenes.
Slimy textured blue colony:
-indicates that a slime layer is being produced from the use of sucrose. - streptococcus species are facultative anaerobes - the innocuotaed plates will be inoculated anaerobically to encourage the bacteria to ferment sucrose.
What bacterial species did you isolate from your mouth throat and skin? What were the gram stain results from the organisms isolated from your body? We're they as expected?
-mouth: streptococcus, lactobacillus, actinomycetes, treponema, fusobacterium. - streptococcus mutans and streptococcus parasanguis are causative agents of dental cavities that colonize the tooth enamel. - streptococcus salivaris colonizes the gum line and saliva. - actually in mouth seen: s. mitis and s. salivarius. and enterococcus. throat: streptococcus, staphylococcus, corynebacterium, neisseria, and haemophilus. - alpha, beta, and gamma hemolytic bacteria. - streptococcus pyogenes: causative agent of strep throat. - skin: staphylococcus, bacillus, streptococcus, propionibacterium, and some micrococcus species - staphylococcus epidermidis and staphylococcus aureus.
What is the countable range and how is it used?
25-250 cfu's, 25 is too few and 250 is too many in order to determine microbial load in sample.
Why are coliforms alone not indicative of the sanitary quality of swimming pools?
A positive test for total coliforms always requires more tests for fecal coliforms or E. coli. A confirmed positive test for fecal coliforms or E. coli means you need to take action as advised by your water system.
Actidione glucose yeast extract agar
ACT, supports the growth of actinomycetes, and the addition of actidione (cyclohexamide) inhibits the growth of saprophytic fungi.
Acquired vs natural resistance
Acquired: resistance develops through mutations - penicillin-binding protein inhibits antibiotics that end in cillin - MRSA: methicillin resistant staph aureus. Methicillin used to treat S aureus infections in 1960, MRSA in 1961. Natural:gram negative tend to be more resistant to antibiotics than gram positive.
Bacteriostatic antibiotics
Antibiotics that do not actually kill bacteria but rather inhibit their growth
Normal body micro flora
Are commensals and colonize many areas of the body. They occupy niches in various habitats within the body and out-compete pathogenic bacteria. However, they may act as opportunistic pathogens and cause disease under some circumstances.
Be able to calculate Cafu/g or Cafu/ml
Average number of colonies/ (dilution of tube)(volume plated)
reduction
gaining electrons or H atoms losing oxygen atoms
Is Mitis Salivarius (MS) Agar selective, differential, or both? For which organism?
Both Selective for Streptococci Differential: Contains trypan blue & tellurite
Ratio of endospore formers to aerobic heterotrophs in soil
Calculate.
Positive control ammonium
Citrobacter Freundii
what is the principal fecal coliform?
E. coli?
Catalase test on blood agar
Ensure you not get red blood cells otherwise false positive
Why might a water company be interested in knowing the source of E coli in a positive sample? (Fecal or soil)?
In order to determine where the source is an stop it from polluting???
nitrifying bacteria
Include the genera Nitrosomonas and Nitrobacter
oxidation
gaining oxygen atoms losing electrons or H atoms
What is the purpose of OPA and TCA reagents
OPA: reacts with ammonium in the broth to form a blue/black color if the microbe is able to hydrolyze peptone and release ammonium into the medium. TCA: protonates ammonia to ammonium increases ammonium in the broth
Know which medium is used for growing which soil bacteria
PCA: aerobic heterotrophs and endospores ACT: actinomycetes Sabourd's agar: fungi
what spectrum of organisms does each antibiotic tested affect: gram positive, gram negative, or both?
Penicillin g: gram positive bacteria Ampicillin: both Tetracycline: both Streptomycin: both
Fungi that produce antibiotics
Penicillium and Cephalosporium
Mouth bacteria
S mitis and s salivarus and enterococcus S mitis: produces small blue colonies 1-2mm S salivarius: produces blue small or blue rough gumdrop colonies 1-5 mm Enterococcus: dark blue to black shiny colonies 1-2 mm in width
What are predominant genera of bacteria found on skin?
Staphylococcus and micrococcus.
Kirby-Bauer Test
The test to determine the efficacy of antibiotics or the antibiotic resistance of bacteria.
Aerobic plate count (APC)
Used to give an estimate of the total number of viable microorganisms per gram of soil.
nitrate reduction
a dissimilatory process that converts nitrate to nitrite using the enzyme nitrate reductase sometimes converted all the way to nitrogen gas.
anammox
anaerobic, ammonium, oxidation by plactomycetes. Oxidation of ammonium to nitrogen gas. cheaper solution to wastewater treatment.
Bacteriocidal agents
antibiotics that kill other microbes
ammonification
conversion of organic nitrogen into ammonium, aka decomposition. fungi and decomposing bacteria
which disinfectant worked best against your bacterium tested? how does this disinfectant work? mode of action
didn't test this in lab don't know
Is blood agar selective, differential, or both?
differential, not selective
potable water
fit to drink
how do organisms obtain nitrogen?
humans/animals: eating other organisms plants: soil bacteria bacteria: nitrogen cycle
antibiotic modes of action
inhibition of cell wall synthesis, inhibition of translation, inhibition of nucleic acid synthesis, and membrane disruption.
- safe water drinking standards
less than 2.2 coliforms/100ml
actinomycetes
like streptomyces and some fungi are significant producers of antibiotics.
determine total dilutions
look up but add 1 ml sample to 9 ml diluent get a 1:10 dilution.
zones of inhibtion
measurements of size of are affected by such factors such as the diffusion rate of the antimicrobial agent and the growth rate of the organism
Plaque assay
method used to measure the number of viral particles present in a sample
4% peptone broth
mix of partially hydrolyzed proteins and serves as a source of organic nitrogen. inoculated with bacteria.
well-aerated soils
nitrate is readily available for for plants to undergo nitrification
nitrogen gas in durham tube
nitrate reduction has occurred
Did you observe any bacterial growth inside of the plaques, if so explain how this could happen.
no idea...
Opportunistic pathogens
normal microbiota that cause disease under certain circumstances. Normal skin commensals enter the blood stream a site where it is not normally found can cause septicemia.
OPA reagent
o-phthaldehyde, the presence of ammonium is detected and a blue-black color change will take place if the bacteria were able to hydrolyze the peptone and release ammonium into the culture media .
Escherichia denitrification
only able to undergo partial denitrification: nitrate to nitrite
assimilatiion
opposite of ammonification. conversion of ammonia or ammonium into organic matter like ATP, amino acid, nucleic acid
What happens after something dies?
organic compounds are made available, decomposers hydrolyze the proteins and nucleic acids into amino acids and nucleosides, which are then assimilated by the decomposers. ammonium is released into the environment. Ammonium is taken up by plants, but other nitrogen forms can not be taken up by plants.
Is mannitol salt agar selective, differential, or both?
selective and differential
What is the nitrogen cycle?
the nitrogen cycle serves to recycle usable forms of nitrogen through the ecosystem, making nitrogen available to a wide variety of microbes, plants, and animals. Bacteria play a major role in the cycling of nitrogen by participating processes, including ammonification, nitrification, denitrification, and nitrogen fixing.
1st step of nitrification
the oxidation of ammonium to nitrite carried out by nitrosomonas species.
2nd step of nitrification
the oxidation of nitrite to nitrate carried out by a nitrobacter species
What is nitrification
the process by which ammonium is oxidized first to nitrite then to nitrate. Nitrate is useful for plants so it is good for soil fertility. Under aerobic conditions.
TCA reagent
trichloric acid: protonates any ammonia in the broth to ammonium. a weak analogue of acetic acid. allows OPA reagent to then react with the ammonium if it is present.
Negative Control ammonium
uninnocuilated peptone broth
