Comparison of Various Phenotypic Methods in Detection of Carbapenemases and Metallo-Beta-Lactamases (MBL) in Carbapenem Resistant Clinlical Isolates of Acinetobacter Species at A Tertiary Care Centre

 carbapenem-resistant strains of Acinetobacter baumannii (A. baumannii) have been reported worldwide over the last decade. Detection of the carbapenemases is crucial to determine the severity of the problem. The aim of our study was to detect Carbapenemase and MBL producing strains among Multidrug Resistant (MDR) Acinetobacter species isolated from clinical specimens in this geographical area by Modified Hodge test (MHT) and Imipenem-EDTA double disc synergy test and their evaluation.

 In this descriptive-prospective study, consecutive, non-duplicate, and resistant-to-carbapenems clinical strains of Acinetobacter species isolated from various clinical samples were included. Antimicrobial sensitivity of Acinetobacter isolates was performed on Mueller Hinton agar plates by Kirby-Bauer disk diffusion method. Carbapenemase production was confirmed by MHT. Confirmation of MBL production was done by subjecting all isolates with positive screen test to combined disc test using imipenem, meropenem, and EDTA. Data analysis was done using Epi Info 7.0. Categorical variables were summarized as frequency and percentage and continuous variables as Mean and SD.

 A total of 312 non-duplicate strains of A. baumannii were isolated, out of which 224 (71.79%) strains were resistant and 88 (28.21%) were sensitive to carbapenem. There was 100% sensitivity to Colistin followed by Tigecycline (79%) whereas high degree of resistance was seen against 2nd and 3rd generation cephalosporins and quinolones (>90%). 82.6% were identified as carbapenemase producers on MHT and on Imipenem-EDTA combined disc test (CDT), 21.4% were found to be positive.

 Our study showed that tests like MHT are equally efficient to detect carbapenemase production, followed by Imipenem-EDTA combined disc test. These tests are cost-effective and easy to perform and may be used routinely to assess whether carbapenemase producers are present or not.