Comparative Evaluation of Four Phenotypic Tests for Detection of Metallo-β-Lactamase and Carbapenemase Production in Acinetobacter baumannii

Abstract

Introduction: Acinetobacter baumannii is an emerging multidrug resistant opportunistic pathogen that causes a variety of nosocomial infections. In recent years, carbapenem resistance in A.baumannii has increased due to Ambler class B Metallo β-lactamases or class D OXA Carbapenemases. Objective: The present study was undertaken to detect and compare the various phenotypic methods for MBL production in nosocomial A.baumannii isolates. Materials and Methods: One hundred sixty eight A.baumannii isolates were subjected to disc diffusion assay. Imipenem resistant isolates were subjected to 4 different phenotypic tests. MBL screening was done by Imipenem-EDTA double disc synergy test, Imipenem-EDTA combined disc test, Modified Hodge test and MBL E-test. Results: Out of 168 A.baumannii isolates, 85 (50.59%) were imipenem resistant. Among these 85 isolates, 57 (67.05%) were MBL positive by DDST, 69 (81.18%) by CDT, 85 (100%) by MHT and all these 85 isolates were confirmed to be MBL positive by MBL E-test method. Conclusion: Combined disc test, Modified Hodge test & E-test are equally effective to detect MBL production. However, considering the cost constraints of E-test, simple MHT and CDT can be used. They are easy, economical and can be incorporated into routine testing in laboratories to monitor the emergence of MBLs in MDR A.baumannii.

Keywords

• mdr acinetobacter baumannii (mdr ab) combined disc test (cdt)
• modified hodge test (mht)
• mbl e-test