The Influence of pH on the Survival and Pathogenicity of Salmonella enteritidis Phage-Type 4

McDermid, Ann Sheena (1998). The Influence of pH on the Survival and Pathogenicity of Salmonella enteritidis Phage-Type 4. PhD thesis The Open University.



An ability to survive the sometimes hostile conditions encountered in food, the environment or a host will be crucial to the pathogenicity of Salmonella enteritidis PT4. Isolates of S. enteritidis and S. typhimurium generally grew under a wider range of stresses when compared to other serotypes of Salmonella; they also survived well in aerosols. S. enteritidis PT4 demonstrated enhanced pH tolerance.

Adverse pH was an important discriminatory factor; as this is frequently experienced in nature, the effect of pH on the physiology, tolerance, pathogenicity and proteome expression of a clinical isolate of S. enteritidis PT4 was investigated further. The pH limits for continuous growth (MGT=6.9h), in a minimal medium supplemented with mucin were pH 4.35 and pH 9.45. The adaptive responses of acid and alkaline grown cells differed. Generally, acid grown cells were more tolerant, demonstrating cross-protection to a range of stress factors. In contrast, growth at pH 9.45 induced sensitivity to some stress factors. Growth at the pH limits reduced the percentage of cells expressing fimbriae and/or flagella, and the carriage of the 38MDa plasmid. Cells grown at pH 4.35 were significantly more virulent, both in terms of the number of deaths and the time to death in a mouse model, when compared to pH 7.10 or pH 9.45 grown cells.

The proteome of S. enteritidis varied with growth pH when assayed by two-dimensional electrophoresis with N-terminal sequence analysis. The changes were predominantly quantitative with few novel proteins being observed. Proteins which were regulated in response to growth pH included the S. enteritidis homologues to enolase, GroEL and a precursor of the leu/ileu/val binding protein of S. typhlmurium or Escherichia coli.

The pH adaptive responses of S. enteritidis PT4 may have a significant role in the life of the cell, by influencing physiology, metabolism, viability and pathogenicity for mice.

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