LOCALIZATION OF THE IN-VIVO EXPRESSION OF P-FIMBRIAE AND F1-FIMBRIAE IN CHICKENS EXPERIMENTALLY INOCULATED WITH PATHOGENIC ESCHERICHIA-COLI

Escherichia coil causing septicemia in poultry often possess F1 (type 1) and/or P fimbriae which may be involved in bacterial colonization a nd infection. To investigate the expression of these fimbriae in vivo, two pathogenic E. coil strains with different fimbrial profiles, TK3 (fim(+)/pap(-)) and MT78 (fim(+)/pap(-)), were administered to 2-week- old chickens by either the intratracheal or caudal thoracic air sac in oculation route. Antibodies specific for native Fl fimbriae were detec ted by ELISA and immunodot in the serum of chickens inoculated with ei ther strain MT78 or strain TK3, irrespective of the route of inoculati on. Antibodies specific for P fimbriae of serotype F11 were detected b y ELISA and immunoblotting in the serum of chickens inoculated by eith er route with strain TK3. F1, but not P fimbriae, were expressed by ba cteria colonizing the trachea of chickens inoculated by the air sac ro ute with strain MT78 or TK3, as demonstrated by examination of frozen tissue sections using immunofluorescence. F1 fimbriae were also expres sed by bacteria colonizing the air sacs and lungs, but not by bacteria in the blood or other internal organs, of chickens inoculated with ei ther strain. P fimbriae were expressed by bacteria colonizing the air sacs, lungs, kidney, blood, and pericardial fluid, but not by bacteria colonizing the trachea, of chickens inoculated with strain TK3. Fimbr iae-like structures were observed by electron microscopy on bacteria a dhering to the epithelial cells of the air sacs of chickens inoculated with strain TK3. These results demonstrate that both strains MT78 and TK3 undergo in vivo phase variation with respect to their fimbrial pr ofiles and site of bacterial colonization in different organs of infec ted chickens and suggest that Fl fimbriae are important for initial ba cterial colonization of the upper respiratory tract whereas P fimbriae are important for later stages of the infection. (C) 1997 Academic Pr ess Limited.