Pre-Lab 11

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Describe the Enterobacteriaceae


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Describe the Enterobacteriaceae

gram-negative bacilli, facultative anaerobes

Name three species of the Enterobacteriaceae that are pathogens. Name the disease that each causes

Klebsiella pneumonia- causes pneumonia shigella dysenteriae- causes shigellosis salmonella typhi- causes typhoid fever

how do these pathogens differ from the non-pathogenic forms?

pathogens do not ferment lactose, but the non-pathogens do ferment lactose

Do all E. coli normally cause disease?


What are MacConkey and EMB agar selective for?

gram-negative rods

What do MacConkey and EMB agar differentiate?

lactose fermenters from non-lactose fermenters

Phenylalanine is broke down into---when bacteria that produce phenylalanine deaminase are grown in culture

phenylpyruvic acid

in the phenylalanine deaminase test, a reagent called ferric chloride is added after incubation. What does a positive reaction look like (color)?

a green color

Name a genus in Enterobacteriaceae that is phenylalanine deaminase positive.

Morganella and Proteus

urea is hydrolyzed into___ and ___

ammonia and carbon dioxide (CO2 and NH3)

Name the exoenzyme studied in the urea hydrolysis exercise


name one genus of bacteria that can hydrolyze urea

Proteus mirabillis

after incubation, how can you tell if a urea slant was inoculated with a urease-positive organism or a urease-negative organism?

if positive that slant turns a pink color

Name the indicator that was added to the urea slant before inoculation

phenol red

This indicator is ___ in a solution below pH 8.4 and ___ above pH 8.4

yellow/orange below pH 8.4; pink/red above pH 8.4

What does the acronym SIM stand for?

Sulfur, Indole, Motility

Name the enzyme responsible for sulfide production

cysteine and thiosulfate

After incubation, how can you tell if a SIM tube had been inoculated with an organism positive for sulfide production?

the SIM media turns black

name a genus in Enterobacteriaceae that is positive for sulfide production

salmonella, shiegella, proteus

How is SIM medium used to determine motility of an organism?

when bacteria is stabbed and incubated, growth would be observed throughout the medium and the medium will appear uniformly cloudy if the organism is motile

Name a genus in Enterobacteriaceae that is motile


in the presence of tryptophanase, tryptophan breaks down into ____ plus ammonia


What does Kovac's reagent indicate?

to detect the presence of indole

after incubation, how can you tell if a SIM tube had been inoculated with an indole-positive organism or an indole-negative organism?

if there is a red color then indole is positve