Bacterial and mycoplasmal flora of the middle ear of laboratory rats with otitis media.

Purulent otitis media was confirmed at necropsy in 35 laboratory rats, 14 of which had shown clinical signs of middle ear infection. The bacterial flora of both the affected and grossly normal middle ears was similar, often mixed, and comprised mainly of Staphylococcus haemolyticus, Pasteurella pneumotropica and Corynebacterium spp. Twenty-one isolates of Mycoplasma spp. were recovered from the middle ears of 11 rats with purulent otitis media and one normal rat. Fourteen of the isolates were further identified as either Mycoplasma arthriditis (eight isolates) or Mycoplasma pulmonis (six isolates). In ears affected with otitis media, mycoplasmas were isolated significantly more often from subclinical than from clinical cases, while Pasteurella pneumotropica was isolated significantly more often from clinical than subclinical cases.