title: Phenotypic and genotypic characterisation of multiple antibiotic-resistant Staphylococcus aureus exposed to subinhibitory levels of oxacillin and levofloxacin.
abstract: The emergence and spread of multidrug resistant methicillin-resistant Staphylococcus aureus (MDR-MRSA) has serious health consequences in the presence of sub-MIC antibiotics. Therefore, this study was designed to evaluate β-lactamase activity, efflux activity, biofilm formation, and gene expression pattern in Staphylococcus aureus KACC 10778, S. aureus ATCC 15564, and S. aureus CCARM 3080 exposed to sublethal concentrations of levofloxacin and oxacillin.
  
  
  
  The decreased MICs were observed in S. aureus KACC and S. aureus ATCC when exposed to levofloxacin and oxacillin, while and S. aureus CCARM remained resistance to streptomycin (512 μg/mL) in the presence of levofloxacin and imipenem (>512 μg/mL) in the presence of oxacillin. The considerable increase in extracellular and membrane-bound β-lactamase activities was observed in S. aureus ATCC exposed to oxacillin (>26 μmol/min/mL). The antibiotic susceptibility of all strains exposed to EPIs (CCCP and PAβN) varied depending on the classes of antibiotics. The relative expression levels of adhesion-related genes (clfA, clfB, fnbA, fnnB, and icaD), efflux-related genes (norB, norC, and qacA/B), and enterotoxin gene (sec) were increased more than 5-fold in S. aureus CCARM. The eno and qacA/B genes were highly overexpressed by more than 12- and 9-folds, respectively, in S. aureus CCARM exposed to levofloxacin. The antibiotic susceptibility, lactamase activity, biofilm-forming ability, efflux activity, and gene expression pattern varied with the intrinsic antibiotic resistance of S. aureus KACC, S. aureus ATCC, and S. aureus CCARM exposed to levofloxacin and oxacillin.
  
  
  
  This study would provide useful information for better understating of combination therapy related to antibiotic resistance mechanisms and open the door for designing effective antibiotic treatment protocols to prevent excessive use of antibiotics in clinical practice.
authors.affiliation: Department of Medical Biomaterials Engineering, Kangwon National University, Chuncheon, Gangwon, 24341, Republic of Korea.
authors.forename: Ara
authors.initials: A
authors.lastname: Jo
authors.affiliation: Department of Medical Biomaterials Engineering, Kangwon National University, Chuncheon, Gangwon, 24341, Republic of Korea. juheeahn@kangwon.ac.kr.|Institute of Bioscience and Biotechnology, Kangwon National University, Chuncheon, Gangwon, 24341, Republic of Korea. juheeahn@kangwon.ac.kr.
authors.forename: Juhee
authors.identifier: 0000-0001-9341-009X
authors.initials: J
authors.lastname: Ahn
mesh_terms: D018829:Adhesins, Bacterial; D001422:Bacterial Adhesion / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics; D018441:Biofilms / Q000254:growth & development; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D003030:Coagulase / Q000235:genetics; D004151:Dipeptides; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial / Q000235:genetics; D005838:Genotype; D015378:Imipenem / Q000494:pharmacology; D064704:Levofloxacin / Q000008:administration & dosage / Q000494:pharmacology*; D026901:Membrane Transport Proteins / Q000235:genetics; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects; D008826:Microbial Sensitivity Tests; D010068:Oxacillin / Q000008:administration & dosage / Q000494:pharmacology*; D010641:Phenotype; D016133:Polymerase Chain Reaction; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics*; D013307:Streptomycin / Q000494:pharmacology; D001618:beta-Lactamases / Q000235:genetics / Q000378:metabolism
chemical_list: D018829:Adhesins, Bacterial; D001426:Bacterial Proteins; C515944:ClfA protein, Staphylococcus aureus; D003030:Coagulase; D004151:Dipeptides; D026901:Membrane Transport Proteins; C099272:QacB protein, Staphylococcus aureus; C434058:clfB protein, Staphylococcus aureus; C419365:phenylalanine arginine beta-naphthylamide; C068498:qacA protein, Staphylococcus aureus; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D064704:Levofloxacin; D015378:Imipenem; D001618:beta-Lactamases; D010068:Oxacillin; D013307:Streptomycin
keywords: Antibiotic resistance; Biofilm; Efflux pump; Gene expression; Lactamase; Levofloxacin; Oxacillin; Staphylococcus aureus