Trends in the Microbial Profile of Bronchoalveolar Lavage Samples from Patients with Lower Respiratory Tract Infections

Introduction: Lower respiratory tract infections (LRTIs) contribute substantially to global morbidity and mortality, with bacterial and fungal causative agents exhibiting regional and temporal variations. Evolving antimicrobial resistance patterns among bacterial pathogens pose challenges to empirical treatment strategies. This study aimed to identify the etiological agents of LRTIs and characterize their antimicrobial resistance profiles. Methods: Bronchoalveolar lavage (BAL) fluid was obtained from adult patients with suspected LRTIs undergoing bronchoscopy at a tertiary care center in India between August 2021 and December 2022, and processed using standard microbiological techniques for bacterial and fungal pathogen identification. Antimicrobial susceptibility testing (AST) was performed on isolated pathogens using the Kirby-Bauer disk diffusion method. Data were analyzed using descriptive statistics with Microsoft Excel. Results: Among 86 BAL samples, 33 (38.4%) yielded positive cultures, with 31 bacterial and 2 fungal isolates. Among the bacterial isolates, Klebsiella pneumoniae was the most frequent organism (36.4%), followed by Acinetobacter spp. (18.2%). The fungal isolates were identified as C. albicans. Among K. pneumoniae isolates, resistance to cephalosporins ranged from 66.7% to 100%, with the lowest resistance observed against piperacillin-tazobactam (25%). Among Gram-negative bacterial isolates, 60% of bacterial isolates were extended-spectrum β-lactamase (ESBL) producers, 36% were metallo β-lactamase (MBL) producers, and 48% were carbapenemase producers. Both C. albicans isolates were susceptible to fluconazole and voriconazole, while one isolate exhibited resistance to itraconazole and the other to ketoconazole. Conclusions: This study found that Gram-negative bacteria were the predominant etiological agents of LRTIs, exhibiting high resistance to commonly used empirical antibiotics, such as cephalosporins and carbapenems. Notably, resistance to aminoglycosides was lower than to cephalosporins and carbapenems, which may warrant further investigation into local prescribing patterns. These findings highlight the variability of antimicrobial susceptibility and emphasize the critical need for accurate clinical and microbiological diagnosis, along with the development of evidence-based institutional antibiotic policies for the empirical management of LRTIs.