Distribution and phenotypic and genotypic detection of a metallo-β-lactamase, CphA, among bacteraemic Aeromonas isolates

Chi Jung Wu, Po Lin Chen, Jiunn Jong Wu, Jing Jou Yan, Chin Chi Lee, Hsin Chun Lee, Nan Yao Lee, Chia Ming Chang, Yu Tzu Lin, Yen Cheng Chiu, Wen Chien Ko

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24 Citations (Scopus)

Abstract

The objectives of the study were to investigate the distribution of cphA-related genes (cphA) encoding a CphA metallo-β-lactamase (MBL) among 51 consecutive Aeromonas blood isolates and to compare different phenotypic methods for detecting CphA. The presence of cphA was detected by PCR. Four phenotypic methods, the imipenem-EDTA combined disc test, imipenem- EDTA MBL Etest, agar dilution test and modified Hodge test (MHT), were used to detect imipenem susceptibility and MBL production. The results showed that 35 (69%) blood isolates had cphA. All (100%) of 16 Aeromonas aquariorum isolates and 12 Aeromonas veronii isolates, and 4 (80%) of 5 Aeromonas hydrophila isolates, carried cphA, but none of 15 Aeromonas caviae isolates did. With the standard inocula, irrespective of the presence or absence of cphA, all but one (50, 98%) isolates were susceptible to imipenem tested by disc diffusion, Etest and agar dilution (10 4 c.f.u. spot inocula), and did not exhibit MBL production by the imipenem-EDTA combined disc test and MBL Etest. By the agar dilution test using large inocula (10 7 c.f.u.), 34 (97%) of 35 cphA + isolates had imipenem MICs of ≥16 μg ml -1, higher than the susceptible breakpoint (4 μg ml -1), and demonstrated positive results for the MHT, while one cphA + and all 17 cphA - isolates had imipenem MICs of ≤4 mg ml -1. In conclusion, the distribution of cphA among aeromonads is species-specific, found in A. aquariorum, A. veronii and A. hydrophila, and the MHT may be a phenotypic screening test for CphA production.

Original languageEnglish
Pages (from-to)712-719
Number of pages8
JournalJournal of Medical Microbiology
Volume61
Issue number5
DOIs
Publication statusPublished - 2012 May

All Science Journal Classification (ASJC) codes

  • Microbiology
  • Microbiology (medical)

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