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

Non-Lactose fermenting Enterobacteriaceae Lactose fermenting Non-Lactose fermenting

Non-Lactose fermenting Salmonella Shigella Proteus Morganella

Shigella Shigellae infect only humans causing bacillary dysentery [ Shigellosis ].

unhygienic conditions poor sanitation

Contaminated food & drink overcrowding

Carry Blair Transport Medium 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

- 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. - Specimens have an alkaline pH unlike those from patients with amoebic dysentery which have an acidic pH.

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]

Salmonellae - Enteric fever [ Typhoid & Paratyphoid]. - Diarrhoeal disease [enterocolitis]. - Bacteraemia.

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 H2S 2- S.Paratyphi A produce red slope yellow butt without H2S production 3- S.Paratyphi B produce red slope yellow butt with high amount of H2S

Proteus - Urinary Tract Infection. ( urine )* - Abdominal & wound Infections. ( Pus )* - Septicaemia. ( blood )* - 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

Vogues Proskauer Test - 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.

Citrate Utilization Test - The test is based on the ability of an organism to use citrate as its only source of carbon. Bacteria that can grow on this medium turn the Bromothymol blue indicator from green to blue.

Indole Production 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.

Urease Test The test organism is cultured in a medium which contains urea and the indicator phenol red. 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.

Biochemical tests of Enterobacteriaceae