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.