Pre-enrich food samples prior to the isolation of Salmonella species using Thermo Scientific™ Oxoid™ Buffered Peptone Water (Dehydrated). Buffered Peptone Water is a non-selective pre-enrichment medium. It also provides conditions for resuscitation of cells that have been injured by processes of food preservation.
Low numbers and/or sub-lethally injured Salmonella spp. cells may be present in a test food sample. Pre-enrichment in non-selective Buffered Peptone Water allows the cells time to repair and multiply before being introduced into a selective culture, improving the chances of recovering Salmonella species from the sample.
It was noted by Edel and Kampelmacher1 that sub-lethal injury to salmonellae may occur in many food processes. In a survey involving isolation of salmonellae from meat that had been artificially contaminated with sub-lethally injured organisms, pre-enrichment in buffered peptone water at 37°C for 18 hours before selection in Brilliant Green Tetrathionate Bile Broth showed superior results compared with a direct selection method.
Sadovski2 reported that, in experiments involving isolation of salmonellae from frozen vegetables, the rapid drop in pH when using lactose broth3 as a pre-enrichment medium was detrimental to the recovery of salmonellae. This was due to the enhanced sensitivity to low pH of freeze-injured salmonellae which may contaminate frozen vegetables. Pre-enrichment with Buffered Peptone Water maintained a high pH over a period of 24 hours of incubation. The vegetable tissue has a low buffering capacity and the medium overcame this problem.
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1. Edel W. and Kampelmacher E.H. (1973) Bull. Wld Hlth Org. 48. 167-174.
2. Sadovski A.Y. (1977) J. Food Technol. 12. 85-91.
3. Angelotti R. (1963) `Microbiological Quality of Foods’ Academic Press, New York, p. 149.