Utility of phenotypic methods in detection of metallo-beta-lactamases in gram-negative bacteria

Abstract

Background: Metallo-beta-lactamases (MBLs)-producing Gram-negative bacilli (GNB) are one of the significant multidrug-resistant pathogens causing healthcare-associated infection (HAI) worldwide. The present study aimed to compare the phenotypic and molecular methods to detect MBLs-producing GNB causing HAI, namely Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa in a tertiary care hospital. Materials and Methods: Antimicrobial susceptibilities were determined for 232 isolates identified during 8 months period, and the Modified Hodge Test confirmed carbapenemases production in carbapenem-resistant isolates as per the Clinical and Laboratory Standards Guidelines 2013. MBLs production was detected by the disc enhancement test (DET), combined disk test (CDT), and polymerase chain reaction (PCR) and statistically analyzed. Results: One hundred (43.1%) isolates were found to be carbapenem-resistant, of which 85% were positive on the Modified Hodge Test. The DET was 96.67%, whereas the CDT was 93.33% sensitive as compared to the PCR. Kappa coefficient ranged from 0.918 to 0.959 for different methods indicating the excellent agreement between the three methods. Conclusion: The DET and CDT showed excellent agreement with molecular methods to detect MBLs-producing isolates. They are easy to perform, inexpensive, and can be routinely used in clinical laboratories.

Keywords

• carbapenem
• metallo-beta-lactamases
• mbl phenotypic comparison