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

[[abstract]]The objectives of the study were to investigate the distribution of cphA-related genes (cphA)encoding a CphA metallo-b-lactamase (MBL) among 51 consecutive Aeromonas blood isolatesand to compare different phenotypic methods for detecting CphA. The presence of cphA wasdetected 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 detectimipenem susceptibility and MBL production. The results showed that 35 (69 %) blood isolateshad 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 Aeromonascaviae isolates did. With the standard inocula, irrespective of the presence or absence of cphA, allbut one (50, 98 %) isolates were susceptible to imipenem tested by disc diffusion, Etest and agardilution (104c.f.u. spot inocula), and did not exhibit MBL production by the imipenem-EDTAcombined disc test and MBL Etest. By the agar dilution test using large inocula (107c.f.u.), 34(97 %) of 35 cphA+isolates had imipenem MICs of ¢ 16 mg ml”1, higher than the susceptiblebreakpoint (4 mg ml”1), and demonstrated positive results for the MHT, while one cphA+and all17 cphA”isolates had imipenem MICs of ¡ 4 mg ml”1. In conclusion, the distribution of cphAamong aeromonads is species-specific, found in A. aquariorum, A. veronii and A. hydrophila, andthe MHT may be a phenotypic screening test for CphA production