Host–Microbe Interactions in Healthy and CSOM-Affected Middle Ears

Chronic suppurative otitis media (CSOM) is a chronic middle ear inflammatory condition due to persistent polymicrobial middle ear infection. The interaction between local immune responses and microbial communities is not well understood, complicating the development of targeted therapies. This study aimed to characterise local immune cell responses and microbial composition in CSOM-affected middle ear mucosa, focusing on <i>Pseudomonas aeruginosa</i> and <i>Staphylococcus aureus</i>. A total of 24 CSOM patients and 22 controls undergoing tympanomastoid surgery participated in this prospective study. Middle ear and mastoid mucosa were collected for histological and microbiological analysis. Bacterial identification was performed using standard culture methods and Vitek MS, while immune cell populations were quantified via immunohistochemistry. Statistical analyses were performed using Kruskal-Wallis and Mann-Whitney tests. Microbiology results identified multiple pathogens in CSOM, including <i>S. aureus</i> and <i>P. aeruginosa</i>, with polymicrobial infections in 10 samples. CSOM patients exhibited significantly elevated immune cells, including CD3⁺, CD20⁺, and CD68⁺ cells, compared to controls. Histological analysis showed Gram-positive bacteria in three mastoid samples, with positive antibody staining for <i>S. aureus</i> (20.8%) and <i>P. aeruginosa</i> (12.5%) in CSOM patients. Controls had no bacterial staining. Intracellular bacteria may evade host defences and reduce antibiotic efficacy, contributing to CSOM persistence. Targeting intracellular pathogens in future treatments, along with studying polymicrobial communities, could improve management strategies.