Comparison of two commercial preparations of buffered peptone water for the recovery and growth of Salmonella bacteria from foods

This study compared the performance of two commercial preparations of buffe red peptone water. Performance was assessed in terms of ability to resuscit ate and recover low numbers of stressed cells, buffering capacity, growth o f Salmonella bacteria in pure culture and growth of Salmonella in food pre- enrichments. Although both the preparations of BPW had similar chemical com positions, differences in their recovery performance were found. Brand A re covered significantly higher numbers of heat-injured Salmonella (mean = 0.5 7 log(10) cfu ml(-1) difference) in pure culture compared with brand B when dealing with very low inoculum levels. Although brand B had higher bufferi ng capacity, the pH at the end of the pre-enrichment was found to be simila r in both media, even in foods such as milk powder which showed the greates t decline in pH. Both brands were comparable in their ability to grow unstr essed Salmonella from different food types. In unstressed cell studies, sim ilar cell numbers were recovered at the end of a 24 h incubation period fro m both media, although brand B yielded a higher biomass. In the food study with unstressed cells, performance was related more to the food type and th e likely association between this and the level and type of competitor orga nisms present, rather than to the brand of medium used.