Prevalence of plasmid-mediated quinolone resistance determinants in Citrobacter freundii isolates from Anhui province, PR China

Abstract

This study was conducted to detect and analyse the presence of plasmid-mediated quinolone resistance (PMQR) determinants [qnr, aac(6')-Ib-cr and qepA] among Citrobacter freundii isolates from patients in Anhui province, PR China. During 2009-2010, 31 C. freundii strains were collected from various hospital units and patient specimens. Using PCR, qnr genes were detected in eight isolates, but aac(6')-Ib-cr and qepA genes were not found. The genes qnrA1, qnrB1, qnrB2, qnrB4, qnrB10 and qnrB24 were present in 6.5, 3.2, 6.5, 3.2, 3.2 and 3.2% of C. freundii isolates, respectively. A new subgene of qnrB variant (qnrB24) was found and identified for what we believe to be the first time. PFGE after XbaI digestion of genomic DNA indicated that qnr-positive strains were not clonally related. Conjugation experiments were conducted to determine whether the qnr-carrying plasmids were self-transferable, and plasmids of transconjugants were extracted and analysed. The qnr genes were transferred from three clinical isolates to their transconjugants. Two qnrA1 genes transferred quinolone resistance with a plasmid of ~11 kb, whilst the size of the plasmid carrying the qnrB4 gene was ~64 kb. The susceptibility of positive isolates and transconjugants was tested using an agar dilution method according to Clinical and Laboratory Standards Institute guidelines, and the MICs of ciprofloxacin and levofloxacin were determined using Etest strips. Most isolates with qnr genes were resistant to fluoroquinolones and other antimicrobial agents. The MICs of transconjugants showed reduced susceptibility to fluoroquinolones.