Enterobacteriaceae

Bacteria belong to this group are:

• Small rods

• Gram –ve

• Facultative anaerobes

•MacConkey agar commonly used for

all members of this group

Enterobacteriaceae

Bacteria belong to this group are:

• Motile except Shigella and Klebsiella

• Non capsulated except Klebsiella

• Non spore forming

• Include: Escherichia coli, Salmonella,

Shigella, Enterobacter, Klebsiella,

Proteus and Serratia

Bile salts and

crystal violet

Lactose

Give the

selectivity to

the media

Kill Gr+ve

just enteric

Gr-ve grow

Give the

differential

characteristic

to the media

To differentiate

between Lac+

and Lac-

bacteria

Neutral red dye as an indicator

MacConkey agar

Lac+ bacteria Lac- bacteria

Ferment lactose

to form acidsUse peptone instead

of lactose

In acidity pH,

indicator color

change to pink

No lactose fermentation,

No acids, colorless

colonies

Bacteria grow on MacConkey agar are either:

Strong Lac+ such as E. coli

Klebsiella, Enterobacter and

Citrobacter

Lac- such as Shigella,

Salmonella and Proteus

Slowly or weakly Lac+

such as Shigella sonnei

Methods of Diagnosis

Enterobacteriaceae

1. Culturing the organism on

selective media

2. Perform biochemical tests

(TSI, enzymatic tests

such as API, Urease and IMViC)

3. Perform serologic

identification

Escherichia coli (E. coli)

Escherichia coli (E. coli)

• Gr-ve, Rod-shape and motile

• Found in the normal part of

human and animal

• Enteric (found in the intestines)

• When E. coli gets out of the

digestive tract it causes urinary

tract infections, traveler's diarrhea

and nosocomial infections

Cultural characteristics of E coli

• Aerobic and facultative anaerobes

• Its colonies are 2- 4 mm in diameter

• Smooth, convex with an entire edge

• β-haemolysis on blood agar

• On MacConkey agar colonies are rose-pink due to

strong lactose fermenting

Biochemical Activities of E coli

1. Ferments glucose and lactose

No H2S and often produce gas

IMViC

2. Positive for indole and methyl red

tests

3. Negative for Voges proskour and

citrate tests

+ + - -

Biochemical activities of E coli

4. Does not produce Dnase

5. Negative for urease test

Klebsiella

Klebsiella

• Gr-ve, rod shaped

• non-motile

• Encapsulated bacterium

• Found in the normal flora of

the mouth, and intestines

• Klebsiella pneumoniae is most

common spp of pathogenic one

Biochemical Activities of Klebsiella pneumoniae

1. Ferments glucose and lactose

but no H2S with gas production

IMViC

2. Indole and methyl red tests

are –ve

3. Citrate and Voges proskour

tests are +ve

- - + +

Biochemical Activities of Klebsiella pneumoniae

4. Urease test +ve

5. Lactose ferment

6. Mucoid on MacConkey agar?

Because of the capsule which is

type D-polysaccharides that is

more dangerous than type

L-polysaccharides because our

body can not recognize it and in

this way it helps the bacteria to

escape from the body defence

system (Immune system)

Proteus

Proteus

Gram -ve rods

Non lactose fermented on

macConkey agar

ferment glucose, produce

gas and H2S

Proteus vulgaris

Proteus mirabilis

Infections: UTI (stone formation), Ear

infection

Proteus

Urease +ve

The production of fishy odor

Motile (swarming phenomena)

Proteus

Cells are highly motile and

often swarm across the

surface of agar plates

Swarming gives rise to a very

thin film of bacteria on the agar

surface but swarming periods

are interrupted with periods

when the cells stop and

undergo a cycle of growth and

division so that colonies have a

distinct zonation

CLED,MacConkey agar (swarming inhibitors media)

Proteus colonies on CLED

appear blueProteus colonies on

MacConkey appear colorless

CLED,MacConkey agar (swarming inhibitor)

CLED (Cystine Lactose Electrolyte Deficient) agar

Is a valuable non-inhibitory growth medium used in the isolation and differentiation of urinary organisms

Being electrolyte deficient prevents the swarming of Proteus species

Cystine promotes the formation of cystine-dependent colonies

Lactose fermenters produce yellow colonies while non-lactose fermenters appear blue

Bromthymol blue is the indicator dye

In macConkey agar (bile salts) inhibit Proteus to swarm

Electrolyte

deficient Lactose

Prevent

swarming

Give the

differential

characteristic

to the media

To differentiate

between Lac+

and Lac-

bacteria

Bromthymol blue as an indicator

Lac+ bacteria Lac- bacteria

Ferment lactose

to form acids, in

acidity pH,

indicator color

change to

Yellow

No lactose

fermentation, No

acids, colonies

appear Blue

CLED