EXPRESSION OF P-FIMBRIAE AND TYPE-1 (F1) FIMBRIAE IN PATHOGENIC ESCHERICHIA-COLI FROM POULTRY

To investigate the expression of P and type 1 (F1) fimbriae in pathogenic avian Escherichia coli, fourteen pap (+)/fim (+) E. coli isolates pathogenic for poultry were grown on four complex or minimal media, and examined for the presence of mannose resistant (MR) and mannose sensitive (MS) hemagglutination (HA), and for P or for type 1 (F1) fimbriae using immunofluorescence, immunodot, and immunoblot. In addition, isolates grown under different culture conditions were examined for adherence to frozen sections of chicken trachea. Twelve of the 14 isolates were divided into three groups based on adhesin expression in the different media. Isolates of all three groups exhibited strong MSHA reactions when cultures were grown serially in static broth, and expressed a subunit protein with an apparent molecular mass of 17 to 18.5 kDa, serologically related to the F1A major fimbrial subunit, There was a good correlation between MSHA and adherence to chicken tracheal sections. Isolates of group I only demonstrated MSHA and expression of F1A fimbriae after growth in static broth, Isolates of group II demonstrated MSHA and expression of F1A fimbriae after growth in all tested media whereas isolates of group III demonstrated expression of F1A fimbriae only after growth in static broth and minimal agar. Only the five group I isolates expressed MRHA associated with P fimbrial adhesins and expressed fimbriae with a major subunit protein of 18 kDa serologically related to the F11 major fimbrial subunit. None of these five isolates grown on complex solid media, where P but not type 1 fimbriae were expressed, adhered to tracheal sections. Results suggest that i) P fimbriae are not readily expressed in vitro by most pap(+)/fim(+) avian E. coli isolates; ii) environmental control of phase variation of type I fimbriae differs among pathogenic avian E. coli; and iii) receptors for type 1, but not for P fimbriae, are present in chicken tracheal mucosa.