Enterobacteriaceae Family:They include large heterogeneous group of gram negative rods whose natural habitat is the intestinal tract of man or animals.

General characteristics:

1- They are short rods with rounded edge 4-5 microns in length,

non-spore formers.

2- All are motile (having peritichous flagellae) except Klebsiella

and Shigella

3- Facultative anaerobes.

4- Oxidase negative and catalase positive.

5- All ferment glucose with acid or acid and gas production and

reduce nitrate to nitrite.

Gram Negative Bacilli

Based on lactose fermentation they are divided into:

Lactose fermenters as: Escherichia coli, Klebsiella pneumoniae, Enterobacter and Citrobacter .

Non-lactose fermenters as: Salmonella, Shigella, Proteus, Morganella, Yersinia, and Serratia.

Enterobacteriaceae

Microscopy:

All Enterobacteriaceae species are Gram's negative short bacilli, and non-spore producers.

All are motile (having peritichous flagellae) except Klebsiella and Shigella.

Enterobacteriaceae

Biochemical identification of Enterobacteriaceae:

Enterobacteriaceae

The API 20 E strips showing the biochemical reactions of two different Enterobacteriaceae species:

An automated

bacterial

identification

System:

Enterobacteriaceae

Escherichia coli:Escherichia coli is a normal flora of human small intestinal tracts.

Some species are pathogenic to man.

- Facultative anaerobic bacterium.

- Metallic green sheen on EMB medium.

- Rose pink colonies on MacConkey’s.

- Indole production: positive.

Enterobacteriaceae

The genus Klebsiella:Klebsiella species are Lactose fermenter that produce mucoid colonies on MacConkey’s agar.Examples:

1- Klebsiella aerogens .

2- Klebsiella pneumonia.

- Mucoid colonies are capsulated;

So it should be stained by Capsule

Stain.

The capsule could be illustrated

microscopically by India Ink

stain.

Enterobacteriaceae

The Genus Salmonella:Salmonella are found in many animals, including poultry, reptiles, rodents, domestic animals, birds, and human.

Serotypes such as Salmonella typhi and Salmonella paratyphi are highly adapted to man.

The most common sources of human infections are poultry, eggs, and dairy products.

Fecal-Oral route of entry is associated with children infection and food poisoning.

Salmonella are non-lactose fermenters, and most strains are H2S producers.

Identification of microbe depends on serotyping reaction with Anti-Salmonella antibodies in vitro.

Enterobacteriaceae

Salmonella species cultivated on XLD agar; the microbe is non-lactose fermenter

And H2S producer. The microbe show positive reaction with polyvalent reagent.

Enterobacteriaceae

The Genus Proteus:Gram’s negative bacilli belong to Enterobacteriaceae.

Non-Lactose fermenters and H2S producers on XLD.

On blood agar, the microbe illustrates swarming growth.

Almost all strains are urease positive.

Enterobacteriaceae

The Genus Pseudomonas:- Gram’s negative short aerobic bacilli. - All species are oxidase positive. - Grape-like odor .- The exopigment production on nutrient agar discriminate this genus from other. (greenish yellowish pyoverdin) .

Pseudomonas

The Vibrios:

- Vibrios are gram-negative comma shaped, curved bacilli, motile with a single polar flagellum ( 2*0.5 micrometer diameter).

- Facultative anaerobes.

- Vibrio cholerae serogroups O1 and O139 are responsible of epidemic cholera.

- Serogroup O1 is non-capsulated while O139 is capsulated.

- They grow on different media at high pH (8.5-9.5) as alkaline peptone water media.

- TCBS is a selective medium.

- Oxidase and Indole positive. - Reduce nitrate to nitrite.

Vibrios

Microscopic and cultural characteristics of Vibrio cholera:

Curved Gram’s negative

bacilli Vibrio’s as seen

microscopically.

Yellow-Mucoid colonies of

Vibrio cholera on TCBS agar.

Vibrios

Coccobacilli:The Genus Brucella:

The organisms are gram-negative non-motile, non-spore forming, non-capsulated short coccobacilli.

They are aerobic bacteria; grow best on liver extract agar.

They are oxidase and catalase positive.

5-10% CO2 is required for primary isolation.

Coccobacilli

The genus includes:

Brucella melitensis:

It is mainly a pathogen of goats and sheep.

It the strain found in the Mediterranean area and Arabian Gulf.

Brucella abortus: infects cattle mainly but can infect other animals as sheep, goats camels, dogs and pigs.

Brucella suis: mainly found in pigs.

Brucella canis: mainly found in dogs.

Coccobacilli

The Pleomorphic Curved S or U-Shaped Bacilli:The Genus Helicobacter and Campylobacter:

Helicobacter pylori :

- Gram’s negative pleomorphic S or U-shaped Bacilli.

- Motile, non-spore formers, and capsulated bacteria.

- Fastidious microbe grow best on Enriched media supplemented by Bovine serum albumin and antibiotics.

- Microaerophilic (5% O2, 10% CO2), acidophilic bacterium,

Optimum Temp is 37 ᵒC.

- Catalase, oxidase, and urease positive.

Electron micrograph

for Helicobacter pylori

Curved Bacilli

Campylobacter jejuni:- Similar microscopic and cultural characteristics of Helicobacter.

- Urease negative.

- Oxidase and catalase positive.

- Optimum growth temp is 42ᵒ C.

Curved Bacilli

Spirochetes:Treponema species, Borrelia species, and Leptospira species

Treponema pallidum:

Microscopy:- Treponema pallidum has a characteristic helical shape, tightly coiled bacilli like

a telephone cord.

- All are Gram’s negative spiral bacilli with endoflagella.

-Because it can not be stained by Gram’s stain;

wet-mount Preparation should be examined by Darkfield microscopy.

Spirochetes

Treponema pallidum show characteristic Corkscrew- like motility with 90 ˚ angulation .

Electron Microscopy Darkfield microscopy

Spirochetes