Enterobacteriaceae II

- Microscopic appearance

- Cultural characteristics

- Biochemical Tests of Enterobacteriaceae (Non-

Lactose fermenters).

- Identification of Enterobacteriaceae using API 20E

Enterobacteriaceae

- Gram negative rods

- Aerobes and facultative anaerobes

- Motile and non-motile

- Oxidase negative

- Reduce nitrate to nitrite

- Ferment glucose with acid production

Enterobacteriaceae

Lactose fermenting Non-Lactose fermenting

Non-Lactose fermenting

Salmonella

Shigella

Proteus

Morganella

Shigella

-Shigellae infect only humans causing

bacillary

dysentery [ Shigellosis ].

poor sanitation

unhygienic conditions

Contaminated food & drink

overcrowding

-A fresh faecal specimen is required to isolate Shigella

species.

-When there is likely to be a delay in the specimen reaching the

laboratory a suitable transport medium must be used to

ensure

viability of the organisms.Carry Blair Transport Medium

- Specimens have an alkaline pH unlike those from patients

with

amoebic dysentery which have an acidic pH.

- faecal specimens may be watery and contain little blood,

mucus,

and pus cells. In the later stages, the specimen may consist

entirely of pus and blood mixed with mucus.

Shigellae are Gram negative rod.

Shigellae are non-motile organisms

On MacConkey agar Shigella species producing pale non-

lactose fermenting colonies.

On KIA (Kligler iron agar) Most strains of Shigellae produce red

slope and yellow butt. [tube No. 2]

- Enteric fever [ Typhoid & Paratyphoid].

- Diarrhoeal disease [enterocolitis].

- Bacteraemia.

Salmonellae

• specimens include blood, faeces, and urine for

culture as follow :-

1- Blood: Organisms can usually be detected during the

first ten days of infection.

*** S. Typhi can be more rapidly and successfully isolated

from

bone marrow than from blood, especially if the patient has

been treated with antibiotics.

2- Faeces: Organisms can usually be isolated from 40–50% of

patients during the second week of infection and from about

80% of patients during the third week. Faecal culture is

useful

for detecting S. Typhi carriers.

3- Urine: Organisms can usually be isolated from about 25% of

patients after the second week of infection.

Salmonellae are Gram negative rods, non-motile.

On Blood agar Salmonellae produce grey-white 2-3 mm in

diameter, non-haemolytic, some strains appear mucoid.

On MacConkey agar Salmonellae produce pale non-lactose

fermenting colonies.

On Deoxycholate Citrate agar (DCA) Salmonellae produce pale colonies have black centres (H2S-producing Salmonellae).

1- S.Typhi produce red slope yellow butt with few amount of H2S2- S.Paratyphi A produce red slope yellow butt without H2S production3- S.Paratyphi B produce red slope yellow butt with high amount of H2S

Proteus

- Urinary Tract Infection. ( urine )*

- Septicaemia. ( blood )*

- Abdominal & wound Infections. ( Pus )*

- Chest infection. ( sputum )*

* Specimens depending on site of infection.

- Proteus is Gram negative rod

Proteus are actively motile

organisms ( swarming

phenomenon)

Proteus are actively motile organisms

On MacConkey agar Proteus are non-lactose fermenting,

producing pale colonies.

Vogues Proskauer Test

- used to detect acetoin in a bacterial broth culture

- The test is performed by adding alpha-naphthol

and potassium hydroxide to the Voges-Proskauer

broth which has been inoculated with bacteria. A

cherry red color indicates a positive result, while a

yellow-brown color indicates a negative result

- digestion of glucose to acetylmethylcarbinol. If glucose is

being broken down, it will react with alpha-naphthol (VP

reagent 1) and potassium hydroxide (VP reagent 2) to form a

red color. Alpha-naphthol and potassium hydroxide are

chemicals that detect acetoin.

Vogues Proskauer Test

- The test is based on the ability of an organism to use citrate

as its only source of carbon.

CitrateUtilization Test

-Bacteria that can grow on this medium turn the

Bromothymol

blue indicator from green to blue.

When bacteria cultured in a medium which contains tryptophan.

Indole production is detected by Kovac’s reagent which contains 4

(p)-dimethylaminobenzaldehyde which reacts with the indole to

produce a red coloured compound.

Indole Production

When the strain is urease producing, the enzyme will break down

the urea (by hydrolysis) to give ammonia and carbon dioxide.

With the release of ammonia, the medium becomes alkaline as

shown by a change

in colour of the indicator to pink-red.

Urease Test

The test organism is

cultured in a medium which

contains urea and the

indicator phenol red.

Biochemical tests of Enterobacteriaceae