Chromosome and plasmid-mediated quinolone resistance mechanism in clinical isolates of Serratia marcescens / 中华检验医学杂志

ABSTRACT

Objective To investigate the prevalence of plasmid-mediated quinolone resistance ( PMQR ) determinants [ qnr,aac ( 6' ) -Ib-cr and qepA ]and mutations in quinolone resistance-determining regions (QRDRs) of gyrA and parC and their association with fluoroquinolone susceptibility in clinical isolates of Serratia marcescens in Anhui.Methods The minimum inhibition concentration ( MIC ) of 104 strains of S.rnarcescens collected from various clinical specimens from 34 hospitals during 2005 to 2010 were determined by agar dilution method.The qnr,aac (6')-Ib,qepA,gyrA and parC genes were screened by polymerase chain reaction (PCR) in 31 strains resistant to ciprofloxacin,and positive results were subsequently confirmed by sequencing.The conjugation experiments were performed for qnr and aac(6')-Ib-cr positive strains.The MIC of S.marcescens isolates,recipient strains and conjugants were tested by agar dilution method for quinolones and other antimicrobial agents.Results Six strains of the 31 S.marcescens isolates harboured qnr and/or aac(6')-Ib-cr genes.Among those 6 strains,2 strains harboured a qnrB6 gene,1 harboured a qnrS2 gene,and 4 harboured aac( 6' ) -Ib-cr,whereas no qnrA-,qnrC- or qnrD-positive isolate was detected.None of the 31 isolates carried the qepA gene.Mutations in the QRDR of gyrA and parC genes were detected in 9 and 7 isolates,respectively.The conjugation experiments were successfully carried out in 5 isolates of 6 PMQR determinants-postive strains.The MIC of conjugants for quinolones were increased evidently compared to recipient strains.Conclusions Chromosome and plasmid-mediated resistance determinants play an important role in quinolone resistance in clinical isolates of S.marcescens.And more important is that the PMQR determinants can be horizontal transmitted.It is necessary to continuously survey and watch for the spread of PMQR in S.marcescens in public health control program.