Escherichia coli - Urinary tract infections. ( urine )* - Infections of wounds, peritonitis, sepsis and toxic shocks. ( pus )* - Meningitis and bacteraemia in neonates. ( CSF & blood )* - Diarrhoeal disease. ( faeces )* * Specimens depending to site of infection.
Gram negative rod, motile. A minority of strains are capsulated.
On Blood agar E. coli produces 1–4 mm diameter mucoid colonies. Some strains are haemolytic.
On MacConkey agar E. coli ferments lactose, producing smooth pink colonies.
On KIA (Kligler iron agar) Most strains of E. coli produce an acid deep and an acid slope with gas production.
- chect infections. ( sputum )* - Infections of wounds. ( pus )* - Urinary tract infection. ( urine )* - rhinoscleroma. ( infected tissues )* * Specimens depending to site of infection. Klebsiellae
Gram negative rod, non-motile.
Klebsiella is usually capsulated.
On Blood agar Klebsiellae produce large grey-white usually mucoid colonies
On MacConkey agar Most klebsiellae are lactose-fermenting, producing mucoid pink colonies.
Citrobacter & Enterobacter - Opportunistic pathogens occasionally isolated from urine, pus, blood and other specimens.
- C.freundii is Gram negative motile rod
On MacConkey agar C.freundii are lactose-fermenting, producing pink colonies.
- E.cloacae is Gram negative motile rod
On MacConkey agar Enterobacter are lactose-fermenting, producing shiny pink colonies.
- 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.
- 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.
When C.tetani is 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.
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. The test organism is cultured in a medium which contains urea and the indicator phenol red.