Prevalence of Moraxella Species Among Lower Respiratory Tract Infections in and Around Kanchipuram

Objective: This study aims to determine the proportion of Moraxella catarrhalis among bacterial isolates recovered from lower respiratory tract specimens and to assess the associated demographic and clinical characteristics, antimicrobial susceptibility pattern, and phenotypic clavulanate synergy positivity. Methods: This prospective observational study was conducted in the Department of Microbiology at Meenakshi Medical College Hospital and Research Institute, Kanchipuram, Tamil Nadu, India, from December 2024 to December 2025. A total of 100 eligible respiratory specimens, including sputum, bronchoalveolar lavage, and bronchial washing samples, were analyzed. M. catarrhalis was identified by conventional phenotypic methods, including the hockey puck test. Antimicrobial susceptibility testing was performed using routine phenotypic methods, and susceptibility results were summarized descriptively. Data were analyzed using IBM SPSS Statistics for Windows, Version 29 (Released 2023; IBM Corp., Armonk, New York), and p < 0.05 was considered significant. Results: Among 100 bacterial isolates recovered from eligible lower respiratory tract specimens, 16 isolates (16.0%) were identified as M. catarrhalis. Overall, isolate distribution differed significantly across organism categories χ² = 17.04, p = 0.009. Among M. catarrhalis isolates, 56.3% occurred in males, and the highest frequency was observed in patients older than 60 years, 37.5%. Chronic obstructive pulmonary disease was the most common associated clinical condition (31.3%), and diabetes mellitus was the most frequent risk factor (43.8%). Ampicillin showed the highest resistance (43.8%), followed by ciprofloxacin (31.3%) and cefotaxime (18.8%). All isolates were susceptible to azithromycin, and 93.8% were susceptible to amoxicillin-clavulanate. One isolate (6.3%) showed clavulanate synergy positivity. Conclusion: M. catarrhalis constituted a clinically relevant proportion of bacterial isolates recovered from lower respiratory tract specimens in this setting. Its isolation was more frequent in older adults and in patients with chronic airway disease and diabetes mellitus. The observed resistance to ampicillin, along with notable resistance to ciprofloxacin and cefotaxime, supports careful laboratory identification and locally guided antimicrobial therapy.