Molecular characteristics of extended-spectrum β-lactamases in clinical isolates of Enterobacteriaceae from the Philippines

Hajime Kanamori, Rizalina B. Navarro, Hisakazu Yano, Lydia T. Sombrero, Ma Rosario Z. Capeding, Socorro P. Lupisan, Remigio M. Olveda, Kazuaki Arai, Hiroyuki Kunishima, Yoichi Hirakata, Mitsuo Kaku

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22 Citations (Scopus)


β-Lactamases, including extended-spectrum β-lactamases (ESBLs) and AmpC β-lactamases, are major resistance mechanisms of Enterobacteriaceae. Emergence of plasmid-mediated quinolone resistance (PMQR) determinants in ESBL-producing isolates poses a global threat. The molecular characterisitcs of ESBL and PMQR determinants in the Philippines are not well characterized. In this study, we investigated ESBLs and AmpC β-lactamases in clinical isolates of Enterobacteriaceae from the Philippines, and analyzed the association between ESBL and PMQR genes. A total of 91 amoxicilin non-susceptible Enterobacteriaceae were collected at the Research Institute for Tropical Medicine of the Philippines from 2006 to 2008. AmpC- or ESBL-producing isolates were screened by detecting a zone diameter for cefoxitin≤14mm or cefpodoxime≤20mm, respectively. Possible ESBL-producing strains were assessed by the ESBL confirmation test of the Clinical and Laboratory Standards Institute. PCR and sequencing were performed to detect the ESBL and PMQR genes. The number of ESBL-producers and AmpC-producers confirmed phenotypically was 17 (18.7%) and 61 (67.0%), respectively. Of 17 phenotypic ESBL-producers, 14 isolates had ESBL genes, including 6 of Escherichia coli, 3 of Enterobacter cloacae, 2 of Enterobacter aerogenes, 2 of Klebsiella pneumoniae, and 1 of Klebsiella ozaenae. Among these isolates, there were 13, 4, and 12 with bla CTX-M, bla SHV, and bla TEM, respectively. Of the bla CTX-M-positive isolates, bla CTX-M-15 shows the highest prevalence, followed by bla CTX-M-3 and bla CTX-M-14. Of 14 ESBL-producers identified by PCR, 4, 6, and 7 isolates were positive for qnrB, qnrS, and aac(6')-Ib-cr, respectively. The frequency of aac(6')-Ib-cr positivity was significantly higher among CTX-M-15-producing isolates. Thus, we identified bla CTX-M, aac(6')-Ib-cr, and qnr in ESBL-producing Enterobacteriaceae from the Philippines, and revealed a significant association between bla CTX-M-15 and aac(6')-Ib-cr. Local epidemiological data are important for implementing appropriate antimicrobial therapy and effective infection control measures. Continuous monitoring of antimicrobial resistance genes in the Philippines will be required.

Original languageEnglish
Pages (from-to)140-145
Number of pages6
JournalActa Tropica
Issue number1-2
Publication statusPublished - 2011 Oct


  • AmpC β-lactamases
  • CTX-M
  • Enterobacteriaceae
  • Extended-spectrum β-lactamase (ESBL)
  • Plasmid-mediated quinolone resistance (PMQR)

ASJC Scopus subject areas

  • Parasitology
  • veterinary (miscalleneous)
  • Insect Science
  • Infectious Diseases


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