Phenotypic Detection Of Extented Spectrum -Lacramase And Carbapenemase Producing Clinical Isolates In A Tertiary Care Hospital Of The Himalayan Region, India

Abstract

Background:  Non-fermenting Gram-negative bacilli (NFGNB)—notably Pseudomonas aeruginosa and Acinetobacter baumannii—are leading causes of healthcare-associated infections (HAIs) and increasingly exhibit carbapenem resistance via carbapenemase production. Region-specific data from Himachal Pradesh are scarce, yet essential for empiric therapy and infection-control planning.

Methods: A hospital-based cross-sectional study was conducted in the Department of Microbiology, Pt. JLNGMC, Chamba (September 2023–August 2024). Consecutive clinical specimens (n=2378) were processed per CLSI-2023. NFGNB were identified by conventional biochemical test . Antimicrobial susceptibility testing (AST) used Kirby–Bauer disc diffusion; colistin MICs were confirmed by broth microdilution. Carbapenemase detection among carbapenem-non-susceptible isolates employed  modified carbapenem inactivation method (mCIM) . Data were analyzed in SPSS v26.

Results: Of 2378 samples, 250 (5.77%) yielded NFGNB: Pseudomonas aeruginosa (60.8%) and Acinetobacter baumannii (32%),  Acinetobacter lwoffi (2.8%) with Stenotrophomonas maltophilia (2.4%) and Burkholderia cepacia (2.9%) less frequent. Urinary tract infection (UTI) and Otitis media (27.6%) were the most common source, followed by pus/wound swabs (19.2%), Respiratory tract infection (16.8%),septicaemia (7.2%). P. aeruginosa showed high resistance to ceftazidime (64.4%), cefepime (61.8%), piperacillin–tazobactam (58.5%) and carbapenems (42–45%), yet retained susceptibility to amikacin (71%) and polymyxins (>97%). A. baumannii exhibited alarmingly high resistance to carbapenems (68–73%) and cephalosporins (>75%), with lower susceptibility to aminoglycosides (≤43%) and fluoroquinolones (<30%); polymyxins remained active in >95%. Overall carbapenem resistance was 51.4%, higher in A. baumannii (72.9%) than P. aeruginosa (42.1%). Phenotypic testing confirmed carbapenemase production in 76% of carbapenem-resistant isolates; metallo-β-lactamases were detected in 43.6%. MDR/XDR/PDR rates were 81.2%/42.7%/3.1% for A. baumannii and 54.6%/18.4%/0% for P. aeruginosa. ICU isolates had greater carbapenem resistance than non-ICU isolates (61.3% vs 39.8%; p<0.05).

Conclusion: NFGNB impose a substantial AMR burden in Himachal Pradesh. Carbapenem resistance—predominantly carbapenemase-mediated—is widespread, with A. baumannii most affected. Therapeutic options are increasingly limited; polymyxins remain reliable but raise toxicity and stewardship concerns. Routine carbapenemase surveillance, robust antimicrobial stewardship, and strengthened infection-prevention strategies are urgently required in resource-limited hospital settings.