Buffered Peptone Water

LAB 46

Description

A pre-enrichment medium design to help sublethally damaged salmonellae recover before introducing them into a selective medium. This nutrient medium is free from inhibitors and is well buffered to maintain the pH at 7.2 for the incubation period. Sublethal injury to salmonellae occurs in many food processes and this pre-enrichment step greatly increases recovery of these organisms.

Method for reconstitution

Weigh 20 grams of powder and disperse in 1 litre of deionised water. Mix to dissolve then distribute into tubes or bottles. Sterilise by autoclaving at 121˚C for 15 minutes.

Appearance: Pale straw, clear liquid.

pH: 7.2 ± 0.2

Minimum Q.C. organisms: E. coli NCIMB 50034

Storage of Prepared Medium: Capped containers - up to 3 months at 15-20˚C in the dark.

Inoculation: Add 25 grams of sample to 225ml of Buffered Peptone Water and homogenise.

Incubation: Aerobically at 37˚C for 18-24 hours.

Subculture: 10ml aliquots in 100ml of Selenite Cystine Broth LAB 55 and 0.1ml into 10ml Rappaport Vassiliadis Medium LAB 86.

References

Edel W. and Kampelmacher E.H. (1973). Bull. Wld Hlth Org. 48: 167-174.

Poemla P.K. and Silliker J.H. (1976) Salmonella in Compendium of Methods for microbiological examination of foods. Am. Pub. Health Ass., Washington.