title: Characterization of chromosomal qnrB and ampC alleles in Citrobacter freundii isolates from different origins.
abstract: The association of ESBLs (extended-spectrum beta-lactamases)/pAmpCs (plasmid-mediated AmpC β-lactamases) with PMQR (plasmid mediated quinolone resistance) in gram-negative bacteria has been of great concern. The present study was performed to characterize the diversity, gene location, genetic context, and evolution of ampC and qnrB alleles in isolates of Citrobacter freundii. Fifteen isolates of C. freundii were identified from a total of 788 isolates of Enterobacteriaceae derived from humans, animals, animal food products, and the environment between 2010 and 2012. Co-existence of qnrB/ΔqnrB with ampC was detected in all C. freundii isolates. Both ampC and qnrB genes were found to be located on the chromosome, but were distantly separated on the chromosome. Seven and six novel alleles were discovered for the 10 ampC and qnrB variants detected in this study, respectively. Phylogenetic analysis showed that the new alleles differed a little from the variants of ampC/qnrB previously described in this genus. The genetic context surrounding ampC genes was AmpR-AmpC-Blc-SugE. However, five different genetic contexts surrounding qnrB/ΔqnrB genes were observed, but they occurred in all cases between the pspF and sapA genes. Additionally, cloning experiments showed that the regions containing different qnrB alleles, even with different genetic contexts, contributed to the reduction of quinolone susceptibility. Our results showed that the chromosomal ampC and qnrB alleles are closely related to C. freundii. However, unlike ampC, qnrB alleles seemed to be related to the genetic contexts surrounding them. The evolution of these two genes in C. freundii isolates might be through different pathways.
authors.affiliation: Laboratory of Veterinary Pharmacology, College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, PR China.
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Liao
authors.affiliation: Laboratory of Veterinary Pharmacology, College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, PR China.
authors.forename: Liangxing
authors.initials: L
authors.lastname: Fang
authors.affiliation: Laboratory of Veterinary Pharmacology, College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, PR China.
authors.forename: Liang
authors.initials: L
authors.lastname: Li
authors.affiliation: Laboratory of Veterinary Pharmacology, College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, PR China.
authors.forename: Jian
authors.initials: J
authors.lastname: Sun
authors.affiliation: Laboratory of Veterinary Pharmacology, College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, PR China.
authors.forename: Xingping
authors.initials: X
authors.lastname: Li
authors.affiliation: Laboratory of Veterinary Pharmacology, College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, PR China.
authors.forename: Muya
authors.initials: M
authors.lastname: Chen
authors.affiliation: Laboratory of Veterinary Pharmacology, College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, PR China.
authors.forename: Hui
authors.initials: H
authors.lastname: Deng
authors.affiliation: Laboratory of Veterinary Pharmacology, College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, PR China.
authors.forename: Qiu'e
authors.initials: Q
authors.lastname: Yang
authors.affiliation: Laboratory of Veterinary Pharmacology, College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, PR China.
authors.forename: Xue
authors.initials: X
authors.lastname: Li
authors.affiliation: Laboratory of Veterinary Pharmacology, College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, PR China; Jiangsu Co-Innovation Centre for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, Jiangsu, PR China. Electronic address: gale@scau.edu.cn.
authors.forename: Yahong
authors.initials: Y
authors.lastname: Liu
mesh_terms: D000483:Alleles; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics*; D002874:Chromosome Mapping / Q000379:methods*; D002876:Chromosomes, Bacterial / Q000235:genetics*; D016971:Citrobacter freundii / Q000145:classification / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification*; D019143:Evolution, Molecular; D005516:Food Microbiology; D014644:Genetic Variation; D006801:Humans; D008826:Microbial Sensitivity Tests; D058889:Molecular Typing; D010802:Phylogeny; D001618:beta-Lactamases / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; C048795:AmpC beta-lactamases; D001618:beta-Lactamases
keywords: AmpC; Chromosome-encoded; Enterobacteriaceae; Fluoroquinolone; PMQR; β-Lactams