P-fimbriae-producing septicaemic Escherichia coli from poultry possess fel-related gene clusters whereas pap-hybridizing P-fimbriae-negative strains have partial or divergent P fimbrial gene clusters

fire organization of P fimbrial gene clusters of 13 papC-hybridizing Escherichia coli strains isolated from poultry with colisepticaemia, five P-fimbriae-expressing (P-positive) and eight P-fimbriae-non-expressing (P-negative), were examined by PCR and by Southern blot hybridization using primers or gene probes specific to the I, B, A, C or G genes. The absence of P fimbrial expression was associated with lack of PCR amplification of one or more of these genes, most commonly the I gene. Restriction endonuclease EcoRI, BamHI or PstI digests of genomic DNA from all strains hybridized with each of the gene probes and demonstrated polymorphisms between P-positive and P-negative strains. PstI digests of DNA from 12 of the 13 strains, when hybridized with the A gene probe, demonstrated a 0.1 kb fragment specific to the felA gene which encodes the major structural protein of F11 fimbriae. Hence, only the P-positive strains contained complete copies of fel-related gene clusters. In contrast, most of the pap-hybridizing P-negative strains contained partial or divergent P fimbrial gene clusters, which explains the lack of P fimbrial expression by these strains.