Alloiococcus otitidis—otitis media pathogen or normal bacterial flora?

Abstract

During the last decade a new potential otitis media pathogen, Alloiococcus otitidis, has been studied. It is still not clear whether this bacterium really is a pathogen, although it has been found in a high percentage of middle ear effusions in children. The present study aimed to investigate the presence of A. otitidis in the nasopharynx and outer ear canals, and to develop a culture method that would make it possible to isolate A. otitidis from these locations. Nasopharyngeal samples (n = 129) from children below 6 years were investigated by conventional culture on blood agar plates with 6% saline and rabbit antisera against A. otitidis, and by a PCR method. In the same way, we investigated 10 samples from vestibulum nasi of healthy persons, 68 samples from outer ear canals of patients with acute or chronic ear problems, and 24 samples from outer ear canals of healthy persons. In a rat model of acute otitis media, we instilled living A. otitidis into rat middle ears through the tympanic bulla and evaluated the outcome clinically by otomicroscopy at days 3, 6 and 14. Of the 129 nasopharyngeal cultures, 9 were positive for A. otitidis by PCR, but none by the culture method. Of the 68 samples from patients with running ears, 4 were positive for A. otitidis by PCR, but none by the culture method. Of the 24 healthy ear canals, 7 were positive for A. otitidis by PCR and 3 of them also by the culture method. No A. otitidis could be found from the vestibulum nasi. The rat experiment showed that the reactions in the middle ears were mild; we could not provoke a purulent acute otitis media in any of the rats. There was a 7% prevalence of A. otitidis in children below 6 years. The highest prevalence (29%) was found in outer ear canals of healthy persons, which strongly suggests that A. otitidis is part of the normal bacterial flora of the outer ear canal. The doubtful pathogenicity is also confirmed by the fact that--in the rat model--A. otitidis elicited only a mild response in the middle ear. It was possible to isolate A. otitidis using a blood agar plate with 6% saline.

Molecular Microbiological Profile of Chronic Suppurative Otitis Media

“…There has been debate about whether members of the bacterial genus Alloiococcus play a role in the pathogenesis of otitis media in children or if they are part of the commensal microbiota (61,62). Using molecular techniques, we found higher relative abundance in CSOM patients with cholesteatoma than in controls or other subject groups.…”

Impact of anaerobic and oligotrophic conditions on survival of Alloiococcus otitidis, implicated as a cause of otitis media

“…These facts, in combination with a very mild reaction in the middle ears of rats reported by Tano et al [19], suggest that A. otitidis is commensal and a part of the normal bacterial flora in the outer ear canals. However, it is possible that A. otitidis translocated to middle ear canals or combination with other bacterial flora could induce an inflammation causing acute otitis.…”

“…Although A. otitidis has been recovered from the middle ear of children with acute otitis media, recent studies showed that A. otitidis was frequently found in the outer ear canals of healthy volunteers [17][18][19]. These facts, in combination with a very mild reaction in the middle ears of rats reported by Tano et al [19], suggest that A. otitidis is commensal and a part of the normal bacterial flora in the outer ear canals.…”

Applicability of PCR-DGGE and 16S rDNA Sequencing for Microbiological Analysis of Otitis Media with Effusion

“…The recovery rate of A. otitidis from MEEs of children with OME has been up to 5% by culture and up to 50% by PCR [7,8]. It was considered as an important middle ear pathogen after its first recovery from OME, but its etiological role in OME has been doubted in more recent studies [11,24]. Bacteroides spp.…”