Bacteriological and Molecular Study of Moraxella catarrhalis Isolated from Respiratory Tract and Middle Ear Infections in Children

Introduction: Moraxella catarrhalis is increasingly recognized as an important pathogen causing respiratory tract and middle ear infections in children. This study aimed to investigate the prevalence, antibiotic resistance patterns, lipooligosaccharide (LOS) serotypes, molecular characteristics, and virulence gene profiles of M. catarrhalis isolated from pediatric patients in Baghdad. Methods: A total of 200 nasopharyngeal and middle ear swab specimens were collected from children aged 6 months to 5 years presenting with acute respiratory tract infections or otitis media in Baghdad hospitals between September 2024 and February 2025. The study included 120 respiratory tract swabs and 80 middle ear swabs. Bacterial isolates were identified using conventional microbiological methods and confirmed by PCR amplification of the copB gene. LOS serotyping was performed using monoclonal antibodies against LOS serotypes A, B, and C. Genetic diversity was assessed by multilocus sequence typing (MLST), and the virulence genes ompE, ompB2, and ompCD were detected by PCR. Antimicrobial susceptibility testing was performed using the Kirby–Bauer disk diffusion method according to CLSI guidelines, and β-lactamase production was determined using the nitrocefin disk test. Results: The overall prevalence of M. catarrhalis was 24.0%, with a higher isolation rate from respiratory tract specimens (29.2%) than middle ear specimens (16.3%). LOS serotype A was the predominant serotype (62.5%). MLST analysis revealed substantial genetic diversity, with ST449 being the most common sequence type (31.3%). The ompE gene was the most frequently detected virulence gene (85%), followed by ompB2 (70%) and ompCD (65%). High resistance was observed to ampicillin (75%) and erythromycin (50%), whereas all isolates were susceptible to ciprofloxacin and ceftriaxone. Conclusion: Moraxella catarrhalis is an important cause of respiratory tract and middle ear infections among children in Baghdad. The predominance of LOS serotype A, the high prevalence of virulence-associated genes, the genetic diversity of circulating strains, and increasing resistance to commonly used antibiotics underscore the need for continuous molecular surveillance and rational antimicrobial use to improve clinical management.