The role of Alloiococcus otitidis in otitis media

Ear infections are a major problem worldwide. In 1995, the annual cost of medical and surgical treatment of otitis media (OM) in the United States was estimated between US$3-4 billion. These infections are a particular problem among Indigenous Australians and lead to problems of hearing loss, impairment of learning, development of speech, and social skills. An epidemiological study of microorganisms present in middle ear effusions of Indigenous and non-Indigenous children with otitis media with effusion (OME) found the major isolate was a rarely isolated species, Alloiococcus otitidis. This collection of isolates (n = 39) provided a unique opportunity to: characterise this “new” pathogen; determine if current routine diagnostic techniques were sufficient to identify A. otitidis; assess antibiotic susceptibilities; determine if it really is “fastidious” and difficult to isolate; assess potential virulence in a model system employing the human monocytic cell line THP-1. This is the first report of A. otitidis in an Australian population. It is the first description of different phenotypes of this species. It refuted the dogma that the organism is fastidious. It assessed the largest number of isolates to date for antibiotic susceptibilities and found a significant proportion (>33%) resistant to macrolide antibiotics. Slow growth of the organism and presence of β-lactamase producing otopathogens (with which it is often identified in ear effusions by molecular methods) might allow it to survive routine antibiotic treatment for ear infections. In contrast to previous reports using type culture collection isolates, the study provided the only assessment of induction of pro-inflammatory cytokines using recent clinical isolates. The findings have implications for future research on the role of A. otitidis in the aetiology of both acute and chronic otitis media; it also has implications for diagnostic microbiology, appropriate treatment of these infections, and development of vaccines against this species.