Buffered Peptone Water is a non-selective medium recommended as a preenrichment medium by the ISO 6579 and ISO 19250 normative for Salmonella detection in food and water respectively and by the ISO 21528 normative for Enterobacteriaceae detection.
A feature common to all selective media is that sublethally injured organisms are not generally detected and therefore a recovery step must be included in examination procedures. This is of importance, particularly in the food industry as various processes such as heat, desiccation, preservation processes, pH changes, etc, cause sublethal injuries to Salmonella. The broth is rich in nutrients and produces high resuscitation rates for sublethally injured bacteria and intense growth.
Changes in pH may cause damages to bacteria growth. Buffered Peptone Water maintains a high pH over the enrichment period via the phosphate buffer system and allows repair of injured cells sensitive to low pH. Pancreatic digest of casein provides nitrogen, vitamins, minerals and amino acids essential for growth. Sodium chloride supplies essential electrolytes for transport and osmotic balance.
Salmonella can be present in food and water in small numbers and are usually found with considerably larger numbers of other Enterobacteriaceae or other families. Pre-enrichment is necessary to allow the detection of small numbers of Salmonella or injured Salmonella.
Buffered Peptone Water is also recommended by the ISO 6887 as a diluent for all enumerations of microorganisms and by the ISO 11290 as a diluent for Listeria monocytogenes enumeration.