17

Enterobacteriaceae

MSc. Sarah Ahmed

• Oxidase Test

Positive
Negative

Pseudomonas

Enterobacteriaceae

Identification of Gram's -ve rods

Nitrate test: +ve further
reduction to N2
Growth on cetrimide agar:
Pale colonies with green
pigmentation


MacConkey’s agar
& TSI

Lactose fermenter

Pink colonies on MacConkey
& acidic butt and slant on TSI
colorless colonies on MacConkey
& acidic butt alkaline slant onTSI

Lactose non-fermenter

IMViC test
& EMB

IMViC

++ - -
& black colonies with metalic shines on EMB

E.coli

IMViC
- - ++
Klebsiella


No H2S production Y/R
(no blacking in TSI)
Y/R H2S production
(blacking in TSI)

Shigella

Urease production

+ve

Proteus

-ve

SS agar

colorless colonies with black centers

Salmonella

O/F test: O+/F-


Motility
Not motile

Motile

Enterobacter

Culture character

Form smooth and round colonies.
Fluorescent greenish colour.
production of fruity odor (grape-like) .
Inability to ferment lactose.

• Pseudomonas

On nutrient agar
Colonies are smooth, large, translucent
Greenish blue diffusible pigment

On blood agar

Grayish colonies
Many are haemolytic
(beta hemolysis).


This picture shows Pseudomonas aeruginosa (on the right) and Shigella dysenteriae (on the left) in blood agar.

On MacConkey agar

Non-lactose fermenting (colourless colonies)

On EMB

Non lactose fermenting

Cetrimide agar

is a type of agar used for the selective isolation of the gram-negative bacterium, Pseudomonas aeruginosa.

As the name suggests, it contains cetrimide, which is the selective agent against alternate microbial flora.

show a characteristic blue-green and yellow-green colour, respectively.