COLONIZATION OF THE TRACHEAL EPITHELIUM OF PIGS BY FILAMENTOUS BACTERIA RESEMBLING CILIA-ASSOCIATED RESPIRATORY BACILLUS

Warthin Starry staining revealed filamentous bacteria colonizing the t racheal epithelium of 41 of 88 (46.6%) pigs submitted for necropsy at 2 midwestern veterinary diagnostic laboratories. The bacteria were int erspersed between and oriented parallel to the cilia. In 4 of 4 coloni zed pig tracheas, filamentous bacteria were demonstrated by transmissi on electron microscopy. The bacteria were approximately the same lengt h and diameter as cilia, and in areas of heavy colonization the bacter ia outnumbered cilia. The filamentous bacteria were similar in locatio n and morphologic characteristics to cilia-associated respiratory (CAR ) bacilli of rats, mice, rabbits, and cattle. Results of immunoperoxid ase staining and polymerase chain reaction analysis indicated that the pig CAR bacillus is a different bacterium than the rat CAR bacillus. Rat CAR bacillus causes chronic respiratory disease in rats and mice. The association, if any, between pig CAR bacillus and swine respirator y disease is unknown.