Effects Of Fluoroquinolone Exposure To Morphology And Expression Of Sigma Factors In Staphylococus Aureus

Abstract

In the face of fluoroquinolones (FQs) stressor, Staphylococcus aureus (S. aureus) alters its morphology and gene expression as indirect adaptive responses resulting in antibiotic resistance. In this study, the effects of continuous FQs exposure on the morphology and gene expression of sigB and sigS were examined between the S. aureus ATCC 29213 and its FQ-exposed strains. Light microscope and scanning electron microscope were used to identify changes in the colony and cell morphology while gene expression levels of sigB and sigS genes were evaluated using RT-qPCR analysis. Results indicated that nearly all FQ-exposed S. aureus strains, on average, experienced a decrease by about 28% in normal colony perimeter, and attained a roughly 22% increase in single-cell size compared to the parent strain. The percentage of small colony variants (SCV) in cultured media of most FQ-exposed strains saw a rise in its figure in comparison with the initial S. aureus strain. Transcriptional analysis reveals that the expression of both sigB and sigS genes were upregulated in FQ-continuously exposed strains on an average of 1.85 and 2.78 fold change respectively. After being subcultured in antibiotic-free media, the previously upregulated strains tended to return to the initial state or even down-regulated in comparison with the initial S. aureus strain. In conclusion, the results illustrated that the expression of sigB and sigS genes was positively associated with cell size and SCV formation. The upregulation of sigB and sigS genes along with the decrease in normal colony perimeter were selective advantages of S. aureus strains under FQ exposure.