Genomic alterations involved in fluoroquinolone resistance development in Staphylococcus aureus.

AIM: Fluoroquinolone (FQ) is a potent antibiotic class. However, resistance to this class emerges quickly which hinders its application. In this study, mechanisms leading to the emergence of multidrug-resistant (MDR) Staphylococcus aureus (S. aureus) strains under FQ exposure were investigated. METHODOLOGY: S. aureus ATCC 29213 was serially exposed to ciprofloxacin (CIP), ofloxacin (OFL), or levofloxacin (LEV) at sub-minimum inhibitory concentrations (sub-MICs) for 12 days to obtain S. aureus -1 strains and antibiotic-free cultured for another 10 days to obtain S. aureus-2 strains. The whole genome (WGS) and target sequencing were applied to analyze genomic alterations; and RT-qPCR was used to access the expressions of efflux-related genes, alternative sigma factors, and genes involved in FQ resistance. RESULTS: A strong and irreversible increase of MICs was observed in all applied FQs (32 to 128 times) in all S. aureus-1 and remained 16 to 32 times in all S. aureus-2. WGS indicated 10 noticeable mutations occurring in all FQ-exposed S. aureus including 2 insdel mutations in SACOL0573 and rimI; a synonymous mutation in hslO; and 7 missense mutations located in an untranslated region. GrlA, was found mutated (R570H) in all S. aureus-1 and -2. Genes encoding for efflux pumps and their regulator (norA, norB, norC, and mgrA); alternative sigma factors (sigB and sigS); acetyltransferase (rimI); methicillin resistance (fmtB); and hypothetical protein BJI72_0645 were overexpressed in FQ-exposed strains. CONCLUSION: The emergence of MDR S. aureus was associated with the mutations in the FQ-target sequences and the overexpression of efflux pump systems and their regulators.

A deletion mutation in nfxB of in vitro-induced moxifloxacin-resistant Pseudomonas aeruginosa confers multidrug resistance.

The modulation of efflux pump functions under fluoroquinolone (FQ) exposure is of great concern as it could result in occurrence of multidrug-resistant (MDR) bacterial strains. In this study, MDR mechanism in Pseudomonas aeruginosa induced via moxifloxacin (MOX) pressure was investigated. After serial MOX [concentration of 0.5 × the minimum inhibitory concentration (MIC)] exposure, the fully susceptible P. aeruginosa ATCC 9027 strain has increased its MIC not only toward MOX (1→128 mg/L) but also to other antibiotics. Furthermore, this MOX-exposed strain did not revert to antibiotic-sensitive phenotype when being cultured in antibiotic-free medium for 12 days. No mutation was observed for FQ-target (gyrA and parC) or most investigated efflux regulatory genes (mexT, mexR, and nalC) except nfxB in which a 100-bp deletion was found. This associated with the elevated expression of multidrug efflux pump operon (mexCD-oprJ) which could directly result in MDR phenotype.

iTRAQ-based proteome analysis of fluoroquinolone-resistant Staphylococcus aureus.

OBJECTIVES: The aim of this study was to compare global protein expression changes during fluoroquinolone (FQ) exposure of Staphylococcus aureus. METHODS: Total protein extracts of wild-type S. aureus ATCC 29213 and six multidrug-resistant (MDR) strains derived from the wild-type under different FQ exposures were analysed using the 8-plex isobaric tag for relative and absolute quantitation (iTRAQ) method combined with LC-MS/MS analysis. Differentially expressed proteins were searched for their Gene Ontology (GO) annotation (UniProt database) and protein-protein interaction network (STRING v.10.0). recA expression was determined by real-time quantitative reverse transcription PCR (qRT-PCR) analysis. RESULTS: Overall, 582 unique proteins were identified at a confidence level of >95% (unused cut-off >1.3). After strict filtering for proteins with significant expression changes in comparison with the wild-type S. aureus ATCC 29213, 147 unique proteins were identified. GO searching showed that development of FQ resistance was associated with altered expression of various proteins involved in the SOS response (RecA), antibiotic resistance (MgrA), pathogenesis (uncharacterised leukocidin-like proteins 1 and 2, immunoglobulin-binding protein Sbi, triosephosphate isomerase, enolase, EsxA, SaeR, SarA, MgrA) and the stress response (alkyl hydroperoxide reductase subunit C, ClpB, ClpC, ClpL, ClpX, HslU, l-lactate dehydrogenase 1 and 2, SAV1710). Network analysis of antibiotic resistance-related proteins identified three major protein clusters involved in metabolic pathways, aminoacyl-tRNA biosynthesis and ribosome structure. qRT-PCR results were consistent with the proteomics data. CONCLUSIONS: Development of resistance to multiple drugs, including FQs, under drug exposure mostly involves upregulation of SOS and stress response proteins.