Purpose: The objective of this study was to evaluate acid resistance of S. aureus strains and to identify genes related to acid tolerance of S. aureus in tomatoes.
Methods: S. aureus strains ATCC13565, ATCC14458, ATCC23235, ATCC27664, and NCCP10826 were habituated in tomato extract at 35°C for 24h, and S. aureus cells were then harvested by centrifugation. The cells of tomato-habituated S. aureus strains and non-habituated S. aureus strains were then exposed to tryptic soy broth adjusted to pH 3.0 for 60 min, and survivals of the strains were enumerated on tryptic soy agar. Total RNA of tomato-habituated (15 and 60 min) and non-habituated S. aureus strains were extracted, and cDNA was then synthesized to evaluate the expression level of acid-shock related genes by quantitative real-time PCR.
Results: After acid challenge, S. aureus ATCC23235 showed the most obvious difference in survival between tomato-habituated and non-habituated S. aureus, and S. aureus ATCC14458 was the second most resistant. Four genes (clpB, zwf, nuoF, and gnd) were selected as acid-shock related genes from tomato-habituated and non-habituated S. aureus, and there was no obvious difference in gene expression levels after 15-min tomato-habituation. However, tomato-habituated S. aureus ATCC23235 showed higher expression of clpB, zwf, nuoF, and gnd genes after 60 min, compared to non-habituated cells.
Significance: These results indicate that different S. aureus strains have different acid stress response in tomato due to higher expression level of clp, zwf, nuoF, and gnd gene.