Growth of Salmonella enterica Serovar Enteritidis PT4 in media containing glucose results in enhanced RpoS-independent heat and acid tolerance but does not affect the ability to survive air-drying on surfaces

The heat and acid tolerance of isolates of Salmonella enterica serovar Enteritidis PT4 was markedly higher if cells were grown to stationary phase in either commercially produced Tryptone Soya (TSBG) or brain - heart infusion (BHI) broth containing glucose than when cells were grown in either nutrient or Tryptone Soya broth without glucose. Differences between the populations were found to be related to the production of acid in either TSBG or BHI which caused the culture media pH values to fall to pH 5·8-4·7 during overnight incubation. This led to habituation, which increased both heat- and acid-tolerance, although there was no effect on the abilities of cells to survive air-drying on surfaces. The acid tolerance mechanisms, induced by fermentative growth in complex media, responsible for survival at pH 2·8, were RpoS-independent. In addition, although growth rates as measured by cfu were essentially the same in all media, optical density measurements were very different, with those of cells in media containing glucose being much higher. This was found to be due to the formation of larger cells by the Salmonella in these media.