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single largest reservoir of microbes in body

large intestine

how microbes shed from body to environment; 20% by volume; 10^11 per gram


most of microbes in feces are this

obligate anaerobes

about 1-5% of feces microbes

facultative anaerobes

facultatively anaerobic, G- rods found in intestines of humans and animals, simple growth requirements


sub-classifications of enteric bacteria

intestinal pathogens, harmless commensals, and opportunistic pathogens

Salmonella and Shigella species, many Yersinia, and some E. coli; cause diarrheal disease worldwide

intestinal pathogens

cause of typhoid

Salmonella typhi

cause of severe dysentry

Shigella and E. coli O157:H7

do not cause disease in normal habitat of intestines but can cause UTIs, septicemia, pneumonia, and other infections in compromised hosts

opportunistic enteric bacteria

genera of opportunistic enteric bacteria

Escherichia, Enterobacter, Klebsiella, Proteus, Serratia, Citrobacter

#1 cause of UTI and nosocomial infections in USA

opportunistic enteric bacteria

used to detect and isolate enteric bacteria from urine, blood and food samples

MacConkey's agar

inhibit growth of non-enteric bacteria on MacConkey's

bile salts

inhibit G+ bacteria on MacConkey's

neutral red and crystal violet dyes

enteric lactose fermenters on MacConkey's

form red or pink colonies

enteric non-lactose fermenters

form transparent, colorless colonies on MacConkey's

used to detect and isolate enteric bacteria from water samples

Levine's Eosin-Methylene Blue agar

inhibit growth of G+ bacteria on EMB

eosin and methylene blue dyes

enteric lactose fermenters on EMB

blue back with green metallic sheen (Escherichia) or dark brown colonies (Enterobacter/Klebsiella)

enteric non-lactose fermenters on EMB

transparent, amber colonies

lactose fermenting enteric bacteria

Escherichia, Enterobacter, Klebsiella

used to detect and isolate Salmonella and Shigella from fecal, food and water samples

Hektoen agar

inhibit growth of non-enteric bacteria on hektoen

bile salts

inhibit growth of G+ bacteria on Hektoen

acid fuchsin and bromthymol blue dyes

inhibits the growth of most enteric bacteria on Hektoen


differential ingredients in Hektoen agar

Ferric ammonium sulfate, lactose, sucrose, salicin

microbes that can ferment at least one of lactose, sucrose, and salicin on Hektoen

orange or yellow colonies

microbes that can't ferment lactose, sucrose, and salicin on Hektoen

greenish-blue (Shigella), black if they produce H2S (most Salmonella)

Why do Salmonella and Shigella grow well on Hektoen agar when most other enterics do not?

They can survive in the Na2S2O3

long test tube with twelve separate compartments of varying media to test for enteric bacteria; gives a series of 5 numbers

Enterotube Multitest System

single tube medium that has phenol red dye, ferrous sulfate, sodium thiosulfate, and three sugars

Triple Sugar Iron agar

test using indole, methyl red, Vokes-Proskauer, and citrate used to differentiate between Escherichia, Enterobacter, and Klebsiella

IMViC test

rapidly ferment lactose to acids and gas; most of facultative flora in large intestine & feces; help indicate fecal contamination; facultatively anaerobic, G- rods; Escherichia, Klebsiella, Enterobacteria


Why is presence of e. coli in water a better indication of fecal contamination than if Klebsiella and Enterobacter were found in water?

E. coli is not a free-living microbe

measures ability of a microbe to produce tryptophanase which breaks tryptophan into indole, pyruvic acid, and ammonia

indole test

detects indole in IMViC test, combines with indole to make a cherry red reaction product

Kovac's reagent

Indole reactions of coliforms

positive: E. coli, negative: Klebsiella and Enterobacter

measures ability of microbe to ferment glucose to stable acidic end products; red at pH 4-5 and yellow at pH 6+

methyl red test

Methyl red reactions of coliforms

Acidic: e. coli, Basic: enterobacter and most klebsiella

measures ability of a microbe to produce acetoin, an intermediate in fermenting glucose to 2,3 butylene glycol

Voges-Proskauer test

detects acetoin in VP test by oxidizing acetoin to diacetyl which reacts with argine to form a pink complex

Barritt's reagent

VP reactions

positive: enterobacter and most klebsiella, negative: E. coli

measures the ability of a microbe to use citrate as its sole carbon source

Simmons citrate test

How is citrate utilization detected?

growth on agar surface, intense blue color of agar

why does the agar turn blue in citrate positive IMViC results?

CO2 production raises pH to alkaline

Simmons citrate reactions

positive: enterobacter and klebsiella, negative: E. coli

agar used for the indole test that also determines motility and H2S production of a microbe

SIM (sulfide, indole, motility) agar

facultatively anaerobic, catalase +, G+, oxidase + cocci that grow in grapelike bunches; found on skin and mucous membranes of humans and animals (moderate in throats); opportunistic pathogens; major cause of nosocomials


most important staphylococcal pathogen that causes many skin problems, meningitis, septicemia, etc; leading cause of infection in surgery, burn, and neonatal care units; drying resistant, antibiotic resistant strain

Staph aureus

Staph that infects wounds and colonizes foreign objects, causes local infection/septicemia

S. epidermis, S. capitis, S. hominis

difference between S. aureus and other Staphylococcus species

it can produce coagulase which clots blood

virulence factors of S. aureus

produces damaging extracellular enzymes/toxins, hemolysins, and sometimes a golden pigment

selective/differential medium for staphylococci

Mannitol Salts Agar

salt in MSA

selective ingredient that selects for salt tolerant bacteria

differential ingredients in MSA

mannitol and phenol red dye

mannitol and phenyl red dye role in MSA

fermented to acids which come from growing colonies; S. aureus diffuses into agar medium surrounding the colony, lowering pH and turning agar yellow

used to ID group A strep


causes 11% of all nosocomial infections; leading cause of in-dwelling device infection/septicemia

coagulase negative staphylococci

predominant microbes in throat, catalase-, oxidase-, aerotolerant, G+ cocci; grow in pairs

a and Y-hemolytic streptococci

catalase+, oxidase-, G+ irregular rods with clubbed ends that form V shapes and are abundant in throat


catalase+, oxidase+, G- coccus that is enhanced with a 10% CO2 atmosphere; grows in pairs and is abundant in throat

Moraxella catarrhalis

B-hemolytic staph

S. aureus

moderate numbers in throat, catalase-, oxidase-, obligately anaerobic, G- rods

Bacteroides, porphyromonas, prevotella

moderate numbers in throat, fastidious catalase+, oxidase+, G- cocci that grow in pairs on chocolate agar in 10% CO2


small numbers in throat, catalase+, oxidase+, oval shaped eukaryotic cells


small numbers in throat, fastidious catalase+, oxidase-, G- rods, grown on chocolate agar in 10% CO2


small numbers in throat, fastidious small, pleomorphic bacteria w/o cell walls; grow slowly into egg shaped colonies


To what groups do most human strep pathogens belong?

B-hemolytic and Lancefield groups A and B

most important streptococcus pathogens within hemolysis groups

a: S. pneumoniae, Y: enterococcus faecalis, B-Group A strep

further testing for B-hemolytic microbes to determine Group A strep identity

gram stain, catalase test, and sensitivity to A taxo disk

G+ coccus, a hemolytic, soluble in bile, inhibited growth by detergent optochin, has quelling reaction (capsule swelling)

S. pneumoniae

key trait used to differentiate staphylococcus and Streptococcus (both G+ cocci)

catalase (staph + and strep -)

enzyme that breaks down hydrogen peroxide; produced by all obligate aerobes/facultative anaerobes (those that carry out cell respiration)


how aerotolerant bacteria and microaerophilic bacteria survive in oxygen that makes H2O2

superoxide dismutase

biochemical marker used in IDing Neiserria and distinguishing Enterobacteriaceae from pseudomonas and other aerobic G- rods found in soil/water

cytochrome oxidase

oxidase reactions

positive: neisseria, pseudomonas aeruginosa negative: enterobacteriaceae

opportunistic pathogen that is common cause of nosocomials, UTIs, wound/skin infections, etc. oxidase+, aerobic, G- in soil and water

pseudomonas aeruginosa

most common cause of diarrheal diseases

infection with enteric pathogen (e.g. typhoid, salmonellosis, cholera, E. coli, polio, etc)

fecal-oral transmission cycle

enteric pathogens shed via feces, new hosts acquire them through contaminated food/water

factors that facilitate fecal-oral transmission

enteric pathogens have simple growth requirements, many human pathogens are normal flora for animals

commonly used bacteria to determine water safety

coliform bacteria

Does Klebsiella and Enterobacter presence in water indicate fecal contamination?

Not always, but likely

examines water sample's ability to ferment lactose to acids and gas

presumptive test

presumptive test

utilizes 3 aliquots of water in triplicates utilizing 10ml lactose broth each and an inverted Durham test tube

positive presumptive test

positive for coliforms if gas bubble fills 10% or more of Durham by 48 hrs at 37C; if none positive, stop test

confirmed test

positive presumptive tubes streaked onto EMB and incubated for 24h at 37C

positive confirmed test

E.coli-blue-black with green metallic sheen; Enterobacteria and Klebsiella-dark brown, colorless after 5 days; non-coliform-transparent, amber color

completed test

positive confirmed colonies subcultured in agar slant, gram stained, and tested for lactose fermenting ability in Brilliant Green Lactose Bile Broth

Positive Brilliant Green Bile Broth

possible fecal coliform/contaminated, and tested for gram stain using agar slant subculture

Short G- rod from +BGBB test

positive-contains fecal coliforms


enzyme produced by some S. aureus penicillin resistant strains; this gene is carried on a plasmid

small circular DNA molecules that replicate independently of cell's chromosome; transfered by conjugation and transformation


transfer of DNA from one cell to another by direct contact


transfer of genes from one cell to another by naked DNA in solution


transfer of DNA from one bacterium to another via bacteriophages


plasmids that carry antibiotic resistance genes


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