An evaluation of the modified carbapenem inactivation method (mCIM) in conjunction with EDTA or sodium mercaptoacetate, for detecting metallo β-lactamase production for Aeromonas species harboring blaCphA.

Abstract

Several Aeromonas species, including Aeromonas hydrophila, have been known to produce CphA, a chromosomal metallo β-lactamase (MBL). We aimed to evaluate the clinical usefulness of modified carbapenem inactivation method (mCIM) in conjunction with EDTA (eCIM) or sodium mercaptoacetate (SMA-mCIM) for MBL-producing Aeromonas species. Fifty-six clinical isolates of Aeromonas species stored at the University of the Ryukyus Hospital were used in this study. The antimicrobial susceptibility testing was performed using a VITEK®2 AST-N404 card (bioMerieux, Marcy-l'Etoile, France) and the results were interpreted according to the CLSI guideline M45 3^rd edition. The carbapenemase genes, namely bla_GES, bla_IMP, bla_KPC, bla_NDM, bla_OXA-48-like, bla_VIM, and bla_CphA, were detected by PCR. The production of carbapenemase was evaluated using the mCIM and the differentiation of MBL was eCIM and SMA-mCIM. The resistance rates to imipenem and meropenem were 21.4% (12/56) and 32.1% (18/56), respectively. The mCIM showed a sensitivity of 100% (33/33 bla_CphA positive isolates) and a specificity of 95.7% (22/23 bla_CphA negative isolates) for the tested isolates. Among the 33 mCIM-positive isolates, 29 (87.9%) for eCIM, and 6 (18.2%) for SMA-mCIM were judged as MBL positive, respectively. It is suggested that the mCIM in conjunction with EDTA is useful for detecting MBL production in Aeromonas species harboring bla_CphA.