BUFFERED PEPTONE WATER

A non-selective pre-enrichment liquid medium for Salmonella detection in foodstuffs and water.

Code: CB1/1016

Typical formula g/l

Peptone	10.00
Sodium chloride	5.00
Disodium phosphate (anhydrous)	3.50
Monopotassium phosphate	1.50

pH 7.2 +/- 0.2

Directions

Suspend 20g in 1000ml of cold distilled water; heat to dissolve, distribute into flasks of suitable capacity and sterilise in the autoclave at 121°C for 20 minutes.

Description

Buffered Peptone Water is a non-selective enrichment broth, recommended for the pre-enrichment of Salmonella in foodstuffs by ISO 6579 and for the non-selective pre-enrichment of Enterobacteriaceae by ISO 8523. It is also suitable for the preparation of stock suspensions of powdered milk, concentrated milk, yoghurt and other dairy products.

Method

For the analysis of water, Harvey recommends the preparation of 25ml aliquots of the medium at double concentration, inoculated with an equal volume of water and incubated for 15 hours at 37°C. The procedure recommended by ISO/DIS 6579:2000, is the following:

Add 25g of sample portion to 225ml of Buffered Peptone Water. If the required test portion is other than 25g, use the suitable quantity of Buffered Peptone Water to yield approximately 1/10 dilution (m/v). Incubate the initial suspension at 37°C for not less than 16 hours and not more than 20 hours. Transfer 0,1ml of the pre-enriched culture to a tube containing 10ml of Rappaport Vassiliadis Soy (RVS) Broth and 1ml to a flask containing 10ml of Mueller Kauffmann Broth (MKB) Incubate the inoculated RVS Broth at 41,5°C +/- 1°C for 24 h +/- 3 hrs

Incubate the inoculated MKB at 37°C +/- 1 for 24 h +/- 3. Using the culture obtained in the RVS Broth inoculate by means of a 3mm loop, a large-size petri dish or two 90mm petri dishes containing XLD Medium . Proceed in the same way from the enrichment tube by inoculating a second plating medium (e.g. Chromogenic Salmonella Agar, or other suitable selective Salmonella plating-out medium chosen by the laboratory). Using the cultures obtained in MKB after 24 hours of incubation, repeat the procedure with the same two selective plating-out media. Invert the dishes and incubate at 37°C for 24 hrs. +/- 3 h. Examine for the presence of typical colonies. For confirmation take from each dish of each selective medium, at least one typical or suspected colony and a further 4 colonies if the first is negative. Streak the selected colonies onto the surface of Nutrient Agar and incubate at 37°C for 24hrs.

User quality assurance (48 h-37°C)

Productivity control

S.enteritidis ATCC 13076: growth

S.typhimurium ATCC 14028: growth

Storage

Dehydrated medium: 15-30°C

User prepared tubes and flasks: 6 months at 2-8°C

References

Harvey R.W.S. and Price T.H. (1977) J. App. Bact. 43, 145-148.

ISO/DIS 6579 Microbiology of food and animal feed stuffs Horizontal method for the detection of Salmonella spp. 2000.

ISO 8523: 1991 - Microbiology- general guidance for the detection of Enterobacteriaceae with pre-enrichment 1991-10-01