A Comparison of Rapid Phenotypic Tests for The Identification of Carbapenamase Production in Gram Negative Isolates

Introduction: CLSI recommends that until laboratories can implement the revised carbapenem MIC interpretive criteria, the Carba NP test (or an alternative confirmatory test for carbapenemases) should be performed when isolates of Enterobacteriaceae are suspicious for carbapenemase production based on imipenem or meropenem MICs of 2–4 μg/mL or ertapenem MIC of 2 μg/mL. CLSI recommends that for isolates that are Carba NP positive, report all carbapenems as resistant, regardless of MIC. If the Carba NP test is negative, interpret the carbapenem MICs using CLSI interpretive criteria as listed in Table 2A in M100-S20 (January 2010). Aim and objectives : To compare different phenotypic methods of carabapenemase detection namely, the CNPtdirect, the Blue-Carba test, the Carbapenem Inactivation Method in comparison to the Modified Hodge test. Material and Methods: The CNPt-direct, the Blue-Carba test, the Carbapenem Inactivation Method in comparison to the Modified Hodge test were performed to detect Carbapenemase production. Results and Analysis: 70 isolates of Klebsiella spp., 26 isolates of E.coli, 52 Pseudomonas spp. and 56 Acinetobacter spp. were compared for carbapenamase production by the various phenotypic methods as described before. Among all the phenotypic tests, the least detection rate for carbapenamase production in comparison with MHT was for the BCT. The rest of the tests showed good correlation with MHT results. Discussion: CNPt-direct and BCT could also be used to quickly identify carbapenem-resistant isolates from critically ill patients, despite their limitation to detect OXA expressing isolates, while the CIM can be used routinely for detection in other clinical isolates in resource limited settings. -------------------------------------------------------------------------------------------------------------------------------------Date of Submission: 1512-2017 Date of acceptance: 22-2-2017 --------------------------------------------------------------------------------------------------------------------------------------