Differentiation of Enterobacteriaceae Flashcards
Test Differentiation of Enterobacter Bacteria
IMVIC (SIM, MR/VP, CItrate)
MAC (MacKonkey Agar))
EMB (Eosin Methylene Blue Agar)
HEA (Hektoen Enteric Agar)
Urea Hydrolysis Test
Phenylalanine Deaminase Test
IMVIC (SIM Tube)
purpose: test for indole/sulfur production and motility
procedure: inoculate tube with needle and incubate for 48 hours at 37 C;
add 10 drops of Kovac’s reagent
organisms: E. coli, K. pneumoniae, E. cloacae
results: red color: indole positive; black color: sulfur positive
if red, bacteria possesses tryptophanase that breaks down tryptophan and produces indole as a byproduct
Results of IMVIC (SIM Test)
E.coli: red; produces indole; motile
K. pneumoniae: no sulfur or indole; nonmotile
E. cloacae: no indole or sulfur production; motile
IMVIC (MR)
after broth inoculation, add 10 drops Methyl Red indicator
organisms: E.coli, K. pneumoniae;
results: red color indicates positive for glucose fermentation using the mixed acid pathway (lowers pH)
IMVIC (MR) results
E.coli (positive)
K. pneumoniae (negative)
IMVIC (Voges Proskauer)
after broth inocultaion, add 6 drops of VP-A mix and then 6 drops of VP-B mix (and then wait 15 minutes)
organisms: E.coli and K.pneumoniae
results: red color indicates glucose fermentation using the butanediol pathway which produces acetoin
IMVIC (Voges Proskauer) results
E.coli (negative)
K. pneumoniae (positive)
Methyl Red
a pH dye indicator, turning red in acidic solutions and yellow in alkaline solutions;
used in microbiology to indicate enteric bacteria like E.coli
Voges Proskauer (VP) Test
used to detect acetoin production during glucose fermentation, involves adding reagents Barritt’s A and B to a bacterial broth culture
Mixed acid pathway
a metabolic process where bacteria ferment glucose under anaerobic conditions, producing a complex mixture of organic acids
Indole production
indicated by a red ring on the surface of the deep after adding Kovac’s reagent
MR-VP Broth
Glucose Phosphate Broth, used for performing the MR & VP tests
A positive result of a VP test
indicated by a formation of a pink-red color over the surface of the medium
A negative result of a VP test
indicated by a lack of a pink-red color over the surface of the medium
IMVIC Citrate Slant
procedure: inocculate slant using a zig-zag pattern
organisms: E.coli and K. pneumoniae
results: a blue color indicates that an organism utilizes citrate as a sole carbon source
MAC (MacKonkey Plate)
selective/differential media;
purpose: this plate only grows gram negative bacterial species and has a speicific composition to test for different qualities;
peptones, lactose, bile salts, crystal violet, neutral red;
differentiates whether bacteria ferments lactose;
organisms: E.coli (green sheen)
results: lactose fermenters will be a pink color, while non-lactose fermenters will be colorless or pale (sometimes yellow)
MAC (MacKonkey Plate) Results
E.coli (positive; ferments lactose)
HE plate (Hektoen Enteric Agar)
selective and differential media;
purpose: contains bile salts that inhibit the growth of non-pathogenic gram negative bacteria and is commonly used for fecal specimens;
lactose, sucrose, salicin, H2S production;
organisms: S. typhimurium
results: sugar fermentation: salmon color colonies
no sugar fermentation: green/blue colonies;
H2S production: black centers of colonies
EMB plate (Eosin Methylene Blue)
selective/differential media;
purpose: this plate only grows gram negative bacterial species and has a specific composition to test for different qualities;
specifically lactose fermentation;
organisms: E.coli (green sheen)
results: non-lactose fermenters: causing colonies to have a dark color
Urea Hydrolysis Test
broth;
purpose: testing for enzyme urease;
organisms: E. coli and P. vulgaris
results: the positive organism can break down urea into carbon dioxide and ammonia;
this changes the pH of the broth turning a pink color
Urea Hydrolysis Test Results
E.coli (negative)
P.vulgaris (positive)
Phenylalanine Deaminase
purpose: testing for specific enzyme;
organisms: E.coli and P.vulgaris;
results: the organism has the enzyme if the slant turns green
Phenylalanine Deaminase Test Results
E.coli (negative)
P.vulgaris (positive)
SIM media
E.coli: red, motile
K. pneumoniae: not black or red, nonmotile
E.cloacae: not black or red; motile
Methyl Red
E.coli: positive; ferments glucose
K. pneumoniae: negative; does not ferment glucose
Voges Proskauer
E.coli: negative;
K. pneumoniae: positive
Citrate Slant
E.coli: negative
K.pneumoniae: positive
MAC (MacKonkey Plate)
E.coli: positive
S. typhymurium: negative
P.vulgaris: negative
EMB (Eosin Methylene Blue) Agar
E.coli: green sheen
Hektoen Enteric Plate
S. typhimurium: green to blue-green colonies with black centers of hydrogen sulfide
Urea Hydrolysis Broth
E.coli: negative
P.vulgaris: positive
Phenylalanine Deaminase
E.coli: negative
P.vulgaris: positive
