Emerging Resistance and Shifting Bacterial Profiles in Lower Respiratory Tract Infections: A Tertiary Care Perspective

Background and objective Lower respiratory tract infections (LRTIs) continue to pose a significant global public health concern, with bacterial agents responsible for a considerable proportion of cases requiring hospitalization and antibiotic treatment. The increasing emergence of antimicrobial resistance (AMR) among respiratory pathogens further complicates disease management and clinical outcomes. This study aimed to identify the bacterial profile of clinical LRTI cases and to determine the antimicrobial susceptibility of the identified pathogens. Materials and methods The study involved laboratory-based investigation of bacterial isolates from hospitalized patients with clinical suspicion of LRTI at Krishna Hospital and Medical Research Center, Karad, India, over one year from May 2024 to May 2025. Clinical specimens, such as endotracheal aspirates, sputum, and pleural fluid samples, were processed according to standard microbiological protocols. Results The study included 120 cases of confirmed LRTI. The 20-29 years age category exhibited the greatest infection burden, representing 35 (29.17%) cases, while the 30-39 years age group followed with 26 (21.67%) cases. Males were more frequently impacted than females, accounting for 77 (64.17%) cases versus 43 (35.83%). Of the 120 bacterial isolates obtained, Pseudomonas spp. were the predominant organism isolated, representing 49 (40.83%) of the isolates, followed by Acinetobacter spp. (n = 39, 32.50%) and Klebsiella species (n = 16, 13.33%), Escherichia coli (E. coli) (6, 5.00%), Streptococcus spp. (n = 5, 4.17%) and Staphylococcus aureus (S. aureus) ( n = 5, 4.17%). Endotracheal tube (ETT) specimens were the main source of isolates (n = 65, 54.17%), followed by sputum specimens (n = 49, 40.83%) and pleural fluid specimens (n = 6, 5.00%). Antimicrobial susceptibility testing (AST) revealed varied susceptibility patterns, with significant resistance noted among the isolates, especially in Gram-negative isolates. Of the 110 Gram-negative isolates, 96 were recognized as multidrug-resistant (MDR). Conclusions This investigation showed that Gram-negative bacterial pathogens dominate LRTI, with Pseudomonas spp. and Acinetobacter spp. being the most commonly isolated species. Most bacterial isolates were recovered from ETT and sputum specimens, underscoring the significance of appropriate diagnostic specimens in the diagnosis of LRTIs. The widespread occurrence of MDR Gram-negative isolates and the significant resistance to commonly used antimicrobial agents highlight the growing challenge of AMR. These results underscore the significance of prompt microbiological diagnosis, regular culture and AST, susceptibility-guided therapy, effective infection control measures, and antimicrobial stewardship initiatives to improve patient outcomes and reduce the transmission of resistant pathogens.