Role of antibiotic stress in phenotypic switching to persister cells of antibiotic-resistant Staphylococcus aureus

초록

Purpose This study was designed to evaluate phenotypic and genotypic properties of persister cells formed by Staphylococcus aureus ATCC 15564 (SA(WT)), oxacillin-induced S. aureus (SA(OXA)), ciprofloxacin-induced S. aureus (SA(CIP)), and clinically isolated multidrug-resistant S. aureus CCARM 3080 (SA(MDR)). Methods The dose-dependent biphasic killing patterns were observed for SA(WT), SA(OXA), SA(CIP), and SA(MDR) in response to twofold minimum inhibitory concentrate (MIC) of ciprofloxacin. The surviving cells of SA(WT), SA(OXA), SA(CIP), and SA(MDR) after twofold MIC of ciprofloxacin treatment were analyzed using a metabolic-based assay to estimate the fractions of persister cells. Results The least persister formation was induced in SA(CIP) after twofold MIC of ciprofloxacin treatment, showing 58% of persistence. The lowest fitness cost of resistance was observed for the recovered persister cells of SA(CIP) (relative fitness = 0.95), followed by SA(MDR) (relative fitness = 0.70), while the highest fitness cost was observed for SA(WT) (relative fitness = 0.26). The mRNA transcripts were analyzed by RT-PCR assay in recovered persister cells pre-incubated with ciprofloxacin. The highest expression levels of stress-related genes (dnaK and groEL) and efflux pump-related genes (mepR, norA, and norB) were observed in the recovered persister cells of SA(OXA) and SA(MDR). Conclusion This study provides valuable information for understanding crosstalk between antibiotic resistance, tolerance, and persistence in different antibiotic-resistant S. aureus strains.

키워드