Kanamycin Aesculin Azide Agar

(K.A.A. Agar)

LAB 106

Description

A selective isolation and enumeration medium for enterococci (Lancefield group D streptococci) in food. Sodium azide and kanamycin provide the selective inhibition required whilst aesculin and iron salts form an indicator system for the presumptive identification of enterococci. Incubation at 42˚C will increase the medium's selectivity.

Method for reconstitution

Weigh 43 grams of powder, disperse in 1 litre of deionised water. Allow to soak for 10 minutes, swirl to mix then sterilise by autoclaving at 121˚C for 15 minutes. Cool to 47˚C, then dispense into Petri dishes.

Appearance: Pale straw, clear.

pH: 7.0 ± 0.2

Minimum Q.C. organisms: E. faecalis NCIMB 50030 E. coli (inhibition)

Storage of Prepared Medium: Plates - up to 7 days at 2-8˚C in the dark.

Inoculation: Surface, spread 0.1ml to 0.5ml over entire surface of plate.

Incubation: 37˚C or 42˚C aerobically for 18-24 hours.

Interpretation: Count all white/grey colonies, approx 2mm diameter, surrounded by a black halo to give presumptive enterococcus/faecal streptococcus count.

References

Mossel, D.A.A., Bijken, P.H.G., Eelderink, I. and van Spreekens, K.A. (1978). Streptococci, edited by Skinner, F. A. and Quesnel, L.B. SAB Symposium Series No. 7 Academic Press, London.