The microbiology of chronic suppurative otitis media

Abstract

Chronic suppurative otitis media (CSOM) is characterised by otorrhoea and chronic inflammation of the middle ear and mastoid. It contributes to a significant disease burden worldwide. The aim of the thesis was to update the current understanding of the microbiology of CSOM. To do this a scoping review of the literature on CSOM microbiology was performed. Majority of studies identified a single microbe that was isolated from the ear canal using swabs and culture-based techniques. An understanding of the demographics of patients with CSOM in New Zealand was obtained by performing a 10-year retrospective study. This showed that the majority of CSOM patients had a low socioeconomic background, minority ethnic groups were overrepresented and hearing loss was common. To investigate the microbiology of CSOM, traditional culture-based and molecular methods were compared in a prospective study using swabs. Bacterial 16S rRNA sequencing identified the polymicrobial nature of CSOM and the presence of a microbiome in healthy ears, previously thought to be sterile. The results from molecular methods did not support culturebased findings. The inflammatory response and the presence of intramucosal bacteria in tissue specimens was investigated for the same cohort. Chronic inflammatory cells and intramucosal bacteria were identified in CSOM subjects, in keeping with the persistent inflammatory state of these patients. Very few studies have investigated the microbiology of CSOM of tissue derived from the primary site of infection in the middle ear. For this reason, tissue specimens of CSOM patients and healthy controls were analysed prospectively to investigate the microbial composition and absolute abundance of clinically relevant bacteria. Droplet digital PCR (ddPCR), amplicon sequencing and multiplex PCR were utilised in this study. The distribution of the bacteria within the tissue was examined using histology and Gram staining. Genera Staphylococcus and Pseudomonas, the main pathogens reported in culture studies, had very low relative abundance. ddPCR also measured very low absolute numbers of Staphylococcus aureus and Pseudomonas aeruginosa. Large groups of Gram-positive cocci were identified and not believed to be genus Staphylococcus. Instead, it is possible that these Gram-positive bacteria were members from the genus Anaerococcus. Conclusion: This thesis challenges some aspects the current understanding of the microbiology of CSOM, which may have some implications for the optimal treatment of this condition.