Characteristics of fimbriae (pili) of septicaemic Escherichia coli isolated from respiratory tract of poultry

The present study was carried out to characterize fimbriae (pili) of avian pathogenic E. coli (APEC). The fimbriated bacteria showed hydrophobic reaction and mannose sensitive haemagglutination reaction which indicates that only type 1pili was present on the isolates and it was of 6-7nm with 18 and 18.2KDa molecular weight. Its immunogenicity was determined by Enzyme Linked Immuno Sorbent Assay (ELISA) and coagglutination test and it was found that pili separated from serotype O1 and O78 gave nearly same level of immunogenicity while that of O2 gave different results from both. Again, O78 antiserum was able to detect 43.2 and 40.8% of field strains of APEC via ELISA and coagglutination whereas O1 antisera could detect 40.5 and 39.1 per cent of field isolates by these two tests. This shows partial homology between epitopes structure of pili found on O1 and O78. Lastly, adherence assay was performed using most pathogenic serotypes viz. O1, O2 and O78 and these isolates were able to adhere on tracheal epithelium and the adherence could be blocked by antifimbrial sera and D-mannose which suggest the protective role of antifimbrial sera.