Early in vivo interactions of Actinobacillus pleuroaneumoniae with tonsilsof pigs

Twenty gnotobiotic piglets were inoculated with 5x10(8) colony forming unit s of an Actinobacillus pleuropneumoniae biotype 1-serotype 9 strain onto th eir tonsils. Five other piglets (controls) were inoculated with phosphate-b uffered saline solution. Pigs were euthanized at 30 min, 90 min, 180 min, 6 h, 9 h, 12 h or 24 h after inoculation. At necropsy, samples were taken fr om the tonsils for bacteriological, histological, immuno-histochemical and electron microscopical examination. A. pleuropneumoniae was isolated from t onsils of all the infected pigs, but not from tonsils of the control pigs. Early after inoculation bacteria were mainly associated with the stratified squamous epithelium and detached epithelial cells. Vacuolization and desqu amation of the epithelium was observed and many transmigrating neutrophils were present. At later times after inoculation, bacteria were found closely associated with the crypt-walls and with detached cells present in the cry pts. A strong neutrophil migration was observed mainly in the deeper parts of the crypts. It is concluded that attachment of A. pleuropneumoniae to to nsillar epithelial cells probably constitutes a first step in establishing bacteria at this body site. (C) 1999 Elsevier Science B.V. All rights reser ved.