Phenotypic and Molecular Characterization of MBL Genes among Uropathogens Isolated in Mumbai City

Aims: Growing incidences of the pathogens producing Metallo-β-lactamases (MBLs) has been observed in many countries including India. They are carbapenemases that are capable of hydrolysing carbapenems that are often considered as a last resort antibiotic, for infections caused by multiple drug resistant bacteria. The objective of the current study was to investigate the prevalence of New Delhi Metallo-β-lactamase (NDM-1) and other MBL producers among 747 uropathogens collected from Mumbai city.

Place and Duration of Study: The current study was carried out at Department of Microbiology, Wilson College, Mumbai 400007 between September 2011- January 2014.

Methodology: The screening of MBL producers was done using phenotypic detection tests such as antimicrobial susceptibility test, Modified Hodge Test and MBL E-Test. Molecular characterization of the test isolates was carried out using Molecular tests like Polymerase chain reaction and Restriction enzyme digestion.

Results: In the current study, 49 MBL producers were obtained, all of which harboured a plasmid of approximately 50 kb size. Polymerase chain reaction showed the presence of blaNDM-1 in 43/49, blaVIM-1 in 3/49, and blaIMP gene in 3/49 MBL producers. Co-production of Extended Spectrum β-Lactamase namely, blaTEM and blaCTX-M genes were also observed among 25/49 MBL producers. Determination of Minimum Inhibition Concentration (MIC) showed only 35/49 MBL producers to be resistant to meropenem, indicating difficulty in routine MBL detection where it is generally carried out as a screening step. Plasmid borne resistance of MBL producers was confirmed by plasmid loss studies. Restriction enzyme analysis carried out with the help of Eco RI, Bam HI and HindIII revealed different band patterns among MBL producers, indicating clonal unrelatedness and more than one source of origin for spread of antibiotic resistance.

Conclusion: The current study may serve as a basis for better understanding of the resistance patterns of MBL producers, and thus restrict the spread of drug resistance.