Prevalence of Metallo Beta-Lactamase in Non-Fermentative Gram-Negative Bacilli from Clinical Isolates by Phenotypic Methods in a Tertiary Care Hospital
Keywords:
Acinetobacter Species, Combination Disk Test (CDT), Double Disk Synergy Test (DDST), Metallo-β-lactamase (MBL), Non-Fermentative Gram-Negative Bacilli (NFGNB), Pseudomonas aeruginosaAbstract
Background: Non-Fermentative Gram-Negative Bacilli (NFGNB), particularly Pseudomonas aeruginosa and Acinetobacter species, are major contributors to hospital-acquired infections and are increasingly associated with multidrug resistance due to Metallo-β-lactamase (MBL) production. These enzymes confer resistance to carbapenems and pose significant therapeutic challenges. Objective: To determine the prevalence of MBL-producing NFGNB from clinical specimens using phenotypic methods in a tertiary care hospital in Chennai. Methods: A cross-sectional study was conducted from August to October 2023, including 148 non- duplicate clinical isolates of NFGNB. Phenotypic detection of MBL was performed using the Combination Disk Test (CDT) and Double Disk Synergy Test (DDST). Antimicrobial susceptibility testing was conducted using the Kirby-Bauer disk diffusion method as per CLSI guidelines. Results: Among the isolates, 51% were Pseudomonas aeruginosa and 49% were Acinetobacter spp. CDT detected MBL production in 63.5% of isolates, while DDST detected 59.5%. MBL production was higher in Acinetobacter spp. (59.5%) compared to P. aeruginosa (40.4%). The kappa value (κ = 0.6–0.7) indicated good agreement between CDT and DDST. High rates of resistance to imipenem and meropenem were noted. COPD emerged as a borderline significant factor (p=0.058) influencing MBL positivity. Conclusion: The high prevalence of MBL-producing NFGNB highlights the urgent need for routine phenotypic screening to guide antimicrobial therapy and implement effective infection control strategies. CDT and DDST remain reliable, cost-effective methods in resource-limited settings. Further molecular studies are recommended for confirmation and surveillance.
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