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The 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 Pstl digests of genomic DNA from all strains hybridized with each of the gene probes and demonstrated polymorphisms between P-positive and P-negative strains. Pstl 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.
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