BACTERIAL-COLONIZATION AND IN-VIVO EXPRESSION OF F1 (TYPE-1) FIMBRIALO ANTIGENS IN CHICKENS EXPERIMENTALLY INFECTED WITH PATHOGENIC ESCHERICHIA-COLI

Escherichia coli strains that cause septicemia of poultry often posses s Fl (type 1) fimbriae (encoded by pil [fim] homologous gene clusters) and/or P fimbriae (encoded by pap homologous gene clusters). These fi mbriae are thought to be involved in infection and colonization. To st udy the dynamics of infection due to E. coli with different virulence determinant profiles and to examine the expression of these fimbriae i n vivo, three pathogenic E. coli isolates-O1 (pil+/pap+), O2 (pil+/pap ), and O78 (pil+/pap+)-were administered intratracheally to 1.5-week-o ld chickens. Chickens were euthanatized from 3 to 144 hr after infecti on. The three isolates caused lesions in 30 to 55% of birds. Colonizat ion rates of the trachea, lungs, internal organs, and pericardial flui d were similar for all three isolates, whereas significant differences among isolates were observed in colonization of the air sacs and bloo d. Bacteria appeared rapidly in the blood, liver, and spleen, whereas presence in the pericardial fluid generally occurred only after 24 hr postinoculation. The dynamics of colonization of the air sacs varied a mong isolates. Immunofluorescence of frozen tissue sections demonstrat ed F1 fimbriae (pil expressed) but not P fimbriae on all three isolate s colonizing the trachea and on the O1 and 078 isolates colonizing the air sacs. Results suggest that Fl fimbriae are involved in the early stages of development of colisepticemia by promoting association of pa thogenic E. coli with the trachea and air sacs of chickens.