Enterobacteriaceae

Family Enterobacteriaceae

Members of the Enterobacteriaceae of veterinary importance:

Family properties:

• Gram – negative rods up to 3 μ m in length,oxidase – negative, have peritrichous flagella
• non – sporing
• Grow well on MacConkey agar because they are not inhibited by the bile salts in the medium
• Mostly strains are opportunistic pathogens, occasionally causing clinical disease in locations other than the alimentary tract.
• Usual habitat- Intestinal tract
• Enterobacteria can be arbitrarily grouped into three categories: major pathogens, opportunistic pathogens and non – pathogens. 
• The major animal pathogens E. coli, Salmonella species and Yersinia species can cause both enteric and systemic disease. 
•  Opportunistic pathogens: –  Proteus species, Enterobacter species, Klebsiella species Some other members of the Enterobacteriaceae.
• Klebsiella is the only NON_MOTILE under this family
• Lactose fermenters form a pink colony due to acid production from Lactose.
• Non-lactose fermenters have pale colonies and are alkaline due to utilisation of peptone.
• Differentiation of Salmonella and E. coli in growth media:

Salmonella: Brilliant green (BG) agar and xylose – lysine deoxycholate (XLD) agar, are used to differentiate Salmonella from other enteropathogens. 

• On BGA , Salmonella colonies and the surrounding medium show a red alkaline reaction. 
• On XLD medium the colonies of most Salmonella serotypes are red (alkaline reaction) with black centers due to hydrogen sulfide (H2S) production.