Enterobacteriaceae

What are Enterobacteriaceae?

Family of organisms
Many part of normal gut microbiota
80% clinically significant Gram-ve bacilli
50% isolates from cases of septicaemia

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What kind of diseases can Enterobacteriaceae cause?

Meningitis
Bacillary dysentery
Typhoid
Gastroenteritis
UTI
PUO
Septicaemia

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What kind of infections do Enteriobacteriaceae account for?

Gram-negative healthcare-associated infections

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What are the three groups that pathogenic members of Enterobacteriaceae are categorised into? 1/3

Coliforms, which rapidly ferment lactose, are part of the normal microbiota and may be opportunistic pathogens.
E.g. Escherichia, Kiebsiella, Enterobacter and Citrobacter

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Coliform opportunists, which do not ferment lactose.
E.g. Proteus, Morganella, Providencia

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True pathogens
E.g. Salmonella, Shigella and Yersinia

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How can we prevent Enterobacteriaceae infections?

Prevention of faecal contamination
Food cooked thoroughly
Good personal hygiene
Proper sewage control
Vaccination

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What are the problems with the identification of Enterobacteriaceae?

Similar in microscopic appearance and staining properties
Many different species in this family can cause similar symptoms.

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What types of culture media are used to culture Enterobacteriaceae?

Blood agar
MacConkey
XLD
CLED

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What type of bacteria is isolated on McConkey agar?

Gram negative enteric bacilli

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What type of media is McConkey agar?

Selective and differential

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How do lactose fermenting strains present on MacConkey agar?

Grow as red/pink and may be surrounded by a zone of acid-precipitated bile. Red colour due to the production of acid from lactose. RED AGAR
E.g. E. coli
A. aerogene

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How do non-fermenting strains present on the agar?

Colourless and transparent. Do not alter the appearance of the medium. COLOURLESS/YELLOW AGAR

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What type of bacteria does XLD isolate?

Salmonella and Shigella

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What type of media is XLD?

Selective and differential

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How does Salmonella present on XLD?

Red colonies, sometimes black centres

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How does Shigella present on XLD?

Red colonies

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What type of media is CLED?

Differential, non-selective

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What type of bacteria is CLED used to isolate?

Urinary pathogens
E.g. Proteus

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What does CLED prevent?

Excessive swarming of Proteus species due to its lack of electrolytes

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How does Proteus present on CLED?

Translucent blue colonies. Blue-green to blue media

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How does E. coli present on CLED?

Bright pink semi-translucent colonies

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What is a positive result of an oxidase test?

Development of a blue colour - oxidase production

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What is a positive result of a catalase test?

Vigorous bubbling indicates the presence of catalase

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Enterobacteriaceae

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