Polyp and fibrous adhesion formation in acute otitis media caused by non-typeable or type b Haemophilus influenzae or Moraxella catarrhalis

Among a variety of other histopathologic changes, polyps and fibrous adhesions are readily formed in the middle ear mucosa during experimental acute otitis media (AOM) caused by Streptococcus pneumoniae. Quantitative studies on experimental AOM caused by other bacteria have shown that some of these histopathologic changes, such as adaptive bone modeling and increase in goblet cell density, differ according to the type of bacteria. This investigation surveys polyp and fibrous adhesion formation in experimental AOM caused by either non-typeable or type b Haemophilus influenzae, or Moraxella catarrhalis. Seventy-five rats were inoculated with 1 of these 3 bacteria (25 rats in each of 3 groups). Five rats from each group were sacrificed on days 4, 8, 16, 60 and 180 post-inoculation. The middle ear mucosae were dissected and histopathologic changes in whole-mount and section preparations were studied using light microscopy. Polyps were found in most ears and in the greatest numbers on the early days; fewer polyps were found on the later days, regardless of the type of bacteria. However, non-typeable and type b H. influenzae induced formation of significantly more polyps than M. catarrhalis. The polyps were primarily located in the epitympanum. Fibrous adhesions were primarily located in the hypotympanum and formed in almost all ears, on all days post-inoculation, regardless of the type of bacteria. Numbers increased to a peak on day 16 and then decreased. Non-typeable and type b H. influenzae induced formation of significantly more adhesions than M. catarrhalis, and the middle ears displayed a higher number of persisting adhesions in the animals inoculated with non-typeable H. influenzae. We conclude that polyps and adhesions are formed in experimental AOM regardless of bacterial type, confirming a pathogenesis based on inflammation. Both types of H. influenzae induce formation of greater numbers of polyps/adhesions than M. catarrhalis, and the non-typeable form causes more adhesive sequelae in the mucosa than the encapsulated type b.