Molecular characterization of piezotolerant and stress-resistant mutants of Staphylococcus aureus

Aims: In the previous work, following a pressure treatment with wild-type Staphylococcus aureus, we obtained piezotolerant isolates showing altered phenotypic characteristics. This work focuses on understanding the genetic background of their altered phenotype. Methods and Results: AK23, a representative piezotolerant isolate was subjected to DNA microarrays, corroborated by PCR product sequencing and revealed 10-gene deletion. All other piezotolerant isolates possessed the mutation encompassing the region from SAR0665 to SAR0674 genes (9351 bp) which was most likely the result of recombination between two homologous loci (ATTGCGGGTG) present in both genes. RNA microarray transcriptomic analysis showed that due to partial deletion of the low-affinity phosphate transporter pitA, the high-affinity PhoU-PstABCS operon was upregulated in AK23 which could be the reason for piezotolerance. Furthermore, AK23 showed low levels of the virulence gene regulator rnaIII resulting in the downregulation of several agr system genes explaining the impaired virulence characteristics of the mutant. Conclusions: Naturally occurring mutations can result in piezotolerance which can be of a concern for high hydrostatic pressure-treated foods. Significance and Impact of the Study: A locus has been identified in piezotolerant S. aureus mutants providing insight into possible mechanisms associated with phenotypic characteristics of S. aureus. Further work should study each individual gene of the locus.

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