Identification, Antibiogram, and Phenotypic Detection of β-Lactamase-Mediated Resistance in Non-Fermenting Gram-Negative Bacilli (NFGNB) from a Tertiary Care Hospital in Mysore

Introduction: Non-fermenting Gram-negative bacilli (NFGNB) are emerging healthcare-associated pathogens whose rapidly escalating antimicrobial resistance poses substantial therapeutic challenges. This study aimed to determine the prevalence and antimicrobial resistance patterns of NFGNB and to detect β-lactamase-mediated resistance mechanisms (extended-spectrum β-lactamase [ESBL], metallo-β-lactamase [MBL], and AmpC) in a tertiary care hospital in Mysore, Karnataka, India. Methods: In this prospective two-month study, NFGNB were isolated from various clinical specimens (blood, pus, urine, synovial fluid, suction catheter tips, and endotracheal aspirates). Blood specimens were inoculated into brain–heart infusion broth and subcultured onto blood agar and MacConkey agar; all other specimens were plated directly and incubated aerobically at ۳۷ °C for ۱۶–۱۸ h. Bacterial identification and antimicrobial susceptibility testing were performed using the BD Phoenix M۵۰ system. Phenotypic detection of ESBL, MBL, and AmpC was carried out using combined disc-based methods, as the Clinical and Laboratory Standards Institute (CLSI) does not provide standardized confirmatory tests for these mechanisms in non-fermenters. Results: Of ۳,۰۰۰ clinical specimens, ۵۰ yielded NFGNB (prevalence, ۱.۷%), with ۶۴% originating from ICUs (۹۵% CI: ۴۹.۲–۷۷.۱%). The predominant species were Pseudomonas putida (۱۸%), Pseudomonas aeruginosa (۱۶%), and Acinetobacter baumannii (۱۶%). P. putida exhibited ۱۰۰% resistance to ceftazidime, cefepime, ciprofloxacin, levofloxacin, piperacillin–tazobactam, tetracycline, and cefotaxime, while amikacin and gentamicin retained activity against ۷۷.۸% and ۸۸.۹% of isolates, respectively. P. aeruginosa showed high resistance to ceftazidime and cefepime (۸۷.۵% each) and to piperacillin–tazobactam and levofloxacin (۷۵% each). A. baumannii was uniformly susceptible to colistin but resistant to most other agents. Phenotypic analysis revealed ESBL production in ۲۸%, MBL production in ۳۴%, and presumptive AmpC production in ۹۲% of isolates, of which ۶۰.۹% were confirmed. Multiple β-lactamase types co-occurred in several isolates. Conclusion: The high prevalence of multidrug-resistant NFGNB, particularly extensively drug-resistant P. putida and carbapenem-resistant Acinetobacter species, underscores the urgent need for strengthened local antimicrobial resistance surveillance, timely identification, and continuous monitoring of resistance trends to guide targeted therapy and improve patient outcomes.

کلیدواژه ها:

Non-fermenting Gram-negative bacilli ، Antimicrobial resistance ، ESBL ، MBL ، AmpC ، β-Lactamase ، Healthcare-associated infection