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.