Study on mechanisms of plasmid-mediated quinolones resistance in Pseudomonas aeruginosa

OBJECTIVE To explore the mechanisms of plasmid-mediated quinolones resistance(PMQR) in Pseudomonas aeruginosa(P.aeruginosa) clinical isolates.METHODS A total of 256 strains of non-repetitive P.aeruginosa isolated from the Third Affiliated Hospital of Sun Yat-sen University between Jan 2010 and Dec 2010 were collected.Minimal inhibitory concentration(MIC) of ciprofloxacin to P.aeruginosa was determined by broth microdilution method.And PMQR gene qnrA,qnrB,qnrC,qnrD,qnrS,aac(6′)-Ib-cr,and qepA of P.aeruginosa clinical isolates were amplified by PCR.Then the PCR positive products were sequenced to identify their genotypes.RESULTS Of 256 strains of P.aeruginosa investigated,there were 65 strains of ciprofloxacin-resistant P.aeruginosa and 180 strains of ciprofloxacin-sensitive P.aeruginosa.The MIC50 and MIC90 were 0.5μg/ml and 16μg/ml,respectively.Among all clinical isolates,qnrA1 gene was detected in 1 strain,and the MIC of ciprofloxacin of the strain was 2μg/ml.The PMQR genes including qnrB,qnrC,qnrD,qnrS,aac(6′)-Ib-cr and qepA were not detected in any of the strains.CONCLUSION This is the first report in China that qnrA1 gene is related to low level resistance to ciprofloxacin in P.aeruginosa clinical isolates.Up to the present day,PMQR has not yet become one of the principal mechanisms of resistance to quinolones in P.aeruginosa.