Research – Desiccation survival in Salmonella enterica, Escherichia coli and Enterococcus faecium related to initial cell concentration and cellular components

Journal of Food Protection

Salmonella enterica is well-known for its ability to survive and persist in low-moisture environments.  Previous studies have indicated a link between the initial cell concentration and the population of Salmonella that survive upon desiccation and subsequent storage; however, how the initial cell concentration affects survival is unknown.  This study examined the basis of this phenomena and whether it occurred in other microorganisms, specifically Shiga toxigenic Escherichia coli (STEC), and Enterococcus faecium . Salmonella, STEC, and E. faecium were grown as lawns on TSAYE and harvested using buffered peptone water (BPW). To determine recovery at different initial cell levels, cultures were diluted to 9, 7, and 5 log CFU/mL and applied to filters.  Filters were dried for 24 h, then stored for 28 d at 25°C/33% RH. During storage, cells were recovered from filters using BPW and cultivated on TSAYE.  Both Salmonella and E. coli , but not E. faecium , showed non-proportional recovery. Less viability remained with lower initial starting population after 24 h desiccation such that ≥10 log CFU/mL were recovered when 11 log CFU/mL was desiccated, but ❤ log CFU/mL were recovered when 5 log CFU/mL was desiccated. Once dried, persistence did not appear affected by initial cell concentration. When dead cells (heat-treated) were added to the diluent, recovery of Salmonella was proportional with respect to the initial cell concentration. To further examine the response on desiccation, Salmonella was diluted in BPW containing one of 11 different test cell components related to quorum sensing or known to affect desiccation resistance to assess recovery and persistence. Of the 11 additions only cell debris fractions, cell-free extract, and peptidoglycan improved recovery of Salmonella . Desiccation survival appears related to cell wall components, however, the exact mechanism affecting survival remains unknown.

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