BIOCHEMICAL TESTS FOR IDENTIFICATION OF ENTEROBACTERIACEAE Flashcards
memorization
Good test to differentiate Enterobacteriaceae from non-fermenters
Cytochrome oxidase test
Cytochrome oxidase positive result:
Maroon-violet color within 30 seconds
Enumerate cytochrome oxidase-positive organisms:
- Campylobacter
- Aeromonas
- Neisseria
- Pseudomonas
- Pasteurella
Mnemonic: “CAN PP”
Positive result in Nitrate reduction test:
Red, or no color after addition of zinc dust
Positive result in Carbohydrate Fermentation test:
With phenol red indicator, change from RED to YELLOW.
A test for slow lactose fermentation (late). Helpful in differentiating Citrobacter (+) from most Salmonella (-)
ONPG test
Positive result in ONPG:
Yellow color
Enzymes present in rapid lactose fermenters:
B-galactosidase
Permease
Enzymes present in late lactose fermenters:
B-galactosidase only
Non-lactose fermenters does not possess B-galactosidase and Permease
Good test to differentiate Salmonella from Shigella:
H2S production test
H2S production test positive result:
Black precipitate
Ratio of sugars present in Triple Sugar Iron (TSI) Agar:”
Glu : Lac: Suc
1:10:10
Growth in the slant is _____ (Aerobic/Anaerobic)
Slant = Aerobic
Growth in the Butt is _____ (Aerobic/Anaerobic)
Butt = Anaerobic
In TSI Agar
Yellow slant =
Pink slant =
Pink Butt =
Yellow Butt =
Yellow slant = lactose/Sucrose fermented (A)
Pink slant = lactose/Sucrose not fermented (K)
Pink Butt = glucose not fermented (K)
Yellow Butt = glucose fermented (A)
In TSI
If only glucose were fermented, the TSI result is:
Glucose only = K/A (Pink/Yellow) or (Alkaline/Acid)
In TSI
If glucose and another sugar (lactose/sucrose) were fermented, the TSI result is:
Glucose + Lactose/Sucrose = A/A (Yellow/Yellow) or (Acid/Acid)
In TSI
Non-fermenters TSI result would be:
Non-fermenters = K/K (Pink/Pink) or (Alkaline/Alkaline)
Difference between Proteus vulgaris and Proteus mirabilis in terms of fermentation
Proteus vulgaris = Sucrose fermenter (A/A)
Proteus mirabilis = Non-sucrose fermenter (K/A)
Citrobacter TSI:
K/A or A/A
Citrobacter is a Late-Lactose-Fermenter. Initially, it’s TSI is K/A . In prolonged incubation, it’s TSI will turn into A/A
Salmonella and Shigella TSI:
Salmonella & Shigella = K/A
Salmonella = K/A with black precipitate (H2S +)
Shigella = K/A; no black precipitate
one way to differentiate Salmonella and Shigella is the H2S production test;
Salmonella (H2S+)
Shigella (H2S-)
Indole positive organisms:
- Morganella
- Proteus vulgaris
- E. coli
- K. oxytoca
- Providencia
- E. tarda
- Citrobacter koseri
- Plesiomonas shigelloides
mnemonic:
“May PEKPEC Po”
Klebsiella oxytoca is the ONLY Indole(+) Klebsiella
another way to differentiate P. vulgaris and P. mirabilis: P. vulgaris is indole (+) while P. mirabilis is indole (-)
P. vulgaris = A/A; indole (+)
P. mirabilis = K/A; indole (-)
Enzyme in bacteria that oxidizes tryptophan in indole medium
Tryptophanase
Test to diffrentiate lactose-fermenting Enterobacteriaceae:
Methyl-Red - Vogues Proskauer
