Study of plasmid-mediated quinolone resistance determinants in Citrobacter freundii / 中华传染病杂志

ABSTRACT

Objectives This study was conducted to detect and analyze the presence of plasmidmediated quinolone resistance (PMQR) determinants [qnr,aac-(6′)-Ib-cr and qepA] among clinical isolates of Citrobacter freundii strains isolated from patients in Anhui,China,and to understand the susceptibility of PMQR positive strains to commonly used antimicrobial agents.Methods During the year 2009,31 Citrobacter strains were collected from the First Affiliated Hospital of Anhui Medical University.Polymerase chain reaction (PCR) was used to detect PMQR genes.Amplicons were purified,sequenced and compared with data from the GenBank.Conjugation experiments were conducted to determine whether the qnr-carrying plasmids were self-transferable.The susceptibility of the positive isolates and transconjugants were tested by agar dilution method according to Clinical and Laboratory Standards Institute (CLSI) guidelines.The minimum inhibitory concentrations (MIC) of ciprofloxacin and levofloxacin were determined by E-test strips.Results Among the 31 Citrobacter strains,the qnr genes were detected in 8 isolates (25.8％),among which,6 carried qnrB.Aac-(6′)-Ib-cr and qepA were not identified in these isolates.The qnr genes were transferred from four clinical isolates to their transconjugants.Sequence analysis identified one novel qnrB variant (qnrB24).The resistant rate of qnr-positive clinical isolates to quinolone was 87.5 ％.Most of them were also resistant to various other antibiotics,including cefotaxime (75.0 ％),amikacin (7.5 ％),ceftazidime (62.5 ％),cefapime (37.5 ％),and gentamycin (87.5 ％).All qnr positive strains were susceptible to imipenem.MIC of all transconjugants showed reduced susceptibility to fluoroquinolones,with MIC increased by 10-23 folds.Conclusions Our study shows that qnr gene has occurred in Citrobacter freundii isolates from Anhui Province,China.QnrB is most prevalent in these isolates.Most qnr positive isolates are resistant to commonly used antimicrobial agents.