Prevalence and Antimicrobial Susceptibility Patterns of Non-fermenting Gram-Negative Bacteria Causing Lower Respiratory Tract Infections: A Retrospective Study.

Background And Objectives: Lower respiratory tract infections (LRTIs) increase the morbidity and hospital bed occupancy. Cases of LRTI due to non-fermenting Gram-negative bacilli (NFGNB) are common in healthcare institutions. The common NFGNB found nowadays are , , and . Prophylactic antibiotic use and frequent antimicrobial susceptibility testing (AST) impact the microbes' antimicrobial sensitivity patterns. We planned this study to estimate the prevalence of LRTI due to NFGNB and the antimicrobial sensitivity patterns of the causative microbes.

Methods: This retrospective study was conducted at Kalinga Institute of Medical Sciences (KIMS), Bhubaneswar, India. We analyzed data of the patients admitted between June 2023 and May 2025. We included female and male adult patients admitted to KIMS with LRTI during the study period. The specimens of bronchoalveolar lavage (BAL) fluid and endotracheal tube (ET) aspirate obtained from the qualified subjects were examined. Pathogenic bacteria were cultivated using enriched and selective media, such as 5% sheep blood agar and MacConkey agar. To identify isolates and evaluate AST, the VITEK 2 system (bioMérieux, Marcy l'Etoile, France) was employed. To analyze the data, we used R software (version 4.4.3; R Development Core Team, Vienna, Austria).

Results: Our hospital admitted 2,389 patients with LRTI during the research period. Of them, 757 (31.69%) patients had a positive culture result for NFGNB, and 362 (47.82%) participants were female. The study population's median age was 44.79 (38.11-66.43) years. We found three non-fermenters: (401, 52.97%), (248, 32.76%), and (108, 14.27%). The samples of  and were highly sensitive to tigecycline. The cases with  were mainly sensitive to aztreonam and demonstrated the least sensitivity to colistin.

Conclusion: The NFGNB encountered in this study were , , and . was highly sensitive to aztreonam. and had maximum sensitivity for tigecycline. Future studies with bigger sample sizes must examine the pathogenic NFGNB causing LRTI and their antimicrobial susceptibility patterns.