A STUDY ON PREVALENCE OF METALLOBETALACTAMASE PRODUCING GRAM NEGATIVE BACILLI IN A TERTIARY CARE HOSPITAL

AIM- To estimate the prevalence of MetalloBeta Lactamase (MBL) producing gram negative bacilli (GNB)isolated from hospitalized patients and to determine the Minimum Inhibitory Concentration (MIC) of these isolates to imipenem. MATERIALS AND METHODS- A total of 3204 GNB were isolated from various specimens over a period of 6 months. These isolates were subjected to antimicrobial susceptibility testing by disc diffusion test as per Clinical and Laboratory Standards Institute(CLSI) guidelines. A total of 1587 isolates which were resistant to ceftazidime were taken up for further study. Modified Hodge Test (MHT) was performed to screen for MBL production by the isolates followed by testing with Combination Disc Test (CDT). Isolates exhibiting an increase in zone size in CDT were identified as MBL producers. MIC of these MBL producing isolates to imipenem was determined by macrobroth dilution method as per CLSI guidelines. Appropriate control strains were used while performing all the tests. RESULTS- Of the 1587 ceftazidime resistant isolates studied, 1301 were members of Enterobacteriaceae, 188 were Pseudomonas aeruginosa and 98 were Acinetobacter baumanii. MHT was positive in 78, 26 and 14 of these isolates respectively. However, only 60 of the 78 Enterobacteriaceae, 12 of the 14 A.baumanii and all 26 P.aeruginosa were identified as MBL producers by CDT. Majority of the MBL producing bacilli were isolated from tracheal aspirates. Escherichia coli was the predominant MBL producing member of Enterobacteriaceae. Significant statistical association was observed between isolates being non-fermenting bacilli and the production of MBL (p value less than 0.0001). Most of the Enterobacteriaceae isolates exhibited MIC of 16-32 mcg per ml to imipenem while most P.aeruginosa and A.baumanii isolates had MIC of 32-64 mcg per ml. The overall prevalence of MBL production in gram negative bacilli was 3.1 percent with the highest prevalence of 8.5 percent being observed in P.aeruginosa followed by 6.4 percent in A.baumanii and 2.2 percent in Enterobacteriaceae. CONCLUSION- The observation of MBL production by various gram negative bacilli emphasizes the need for regular screening of ceftazidime resistant isolates for possible production of MBL. This would help in guiding patient therapy and institute appropriate infection control measures.