High prevalence of extended-spectrum β-lactamases and qnr determinants in citrobacter species from japan: Dissemination of CTX-M-2

Hajime Kanamori, Hisakazu Yano, Yoichi Hirakata, Shiro Endo, Kazuaki Arai, Miho Ogawa, Masahiro Shimojima, Tetsuji Aoyagi, Masumitsu Hatta, Mitsuhiro Yamada, Katsushi Nishimaki, Miho Kitagawa, Hiroyuki Kunishima, Mitsuo Kaku

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)


Objectives: Extended-spectrum β-lactamases (ESBLs) have become a problem among AmpC-producing Enterobacteriaceae and the emergence of concomitant quinolone resistance in β-lactamase-producing isolates poses a global threat. In this study we investigated the prevalence and regional variation of ESBLs in Japanese clinical isolates of Citrobacter spp. and analysed plasmid-mediated quinolone resistance (PMQR) determinants in ESBL-producing Citrobacter spp. Methods: A total of 348 clinical isolates of Citrobacter spp. collected throughout Japan were studied. Screening and the boronic acid disc test were performed to detect ESBLs in Citrobacter spp. with chromosomal AmpC β-lactamases. PCR and sequencing were done to identify ESBL and PMQR genes. For ESBL-producing Citrobacter spp., PFGE was performed using the SfiI restriction enzyme. Results: The number of ESBL-producing isolates confirmed phenotypically was 67 (19.3%). The prevalence of ESBL-producing Citrobacter koseri was significantly higher (32.1%) than that of ESBL-producing Citrobacter freundii (4.6%) (P < 0.01). Moreover, the prevalence of ESBLs was notably higher among C. koseri from southern Japan (60.0%). CTX-M-2 was predominant in C. koseri. Of the ESBL-producing C. koseri analysed, 23.2% possessed PMQR determinants, and there was a significant association between qnrB4 and bla SHV-12. The 57 ESBL-producing Citrobacter spp. possessing bla CTX-M, bla SHV or bla TEM were divided into 18 unique PFGE types. Conclusions: This is the first report about the prevalence of PMQR determinants among ESBL-producing Citrobacter spp. from Japan. Our data suggest that ESBLs and PMQR determinants are spreading among C. koseri in Japan.

Original languageEnglish
Article numberdkr283
Pages (from-to)2255-2262
Number of pages8
JournalJournal of Antimicrobial Chemotherapy
Issue number10
Publication statusPublished - 2011 Oct


  • AmpC β-lactamases
  • Enterobacteriaceae
  • PMQR
  • Plasmid-mediated quinolone resistance


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