Analysis of the fim cluster of an avian O2 strain of Escherichia coli: Serogroup-specific sites within fimA and nucleotide sequence of fimI

Escherichia coli MT78, an avian pathogenic strain of serogroup O2, produces a variant form of type 1 fimbriae with distinct antigenic properties and apparent mol. wt of the major subunit, The fim gene cluster of strain MT78 was cloned and its sequence was determined in a region spanning upstream of fimB to the beginning of fimD. Whereas most genes were well conserved relative to fim genes previously described, comparison of the fimA gene from strain MT78 with homologous sequences from other strains of E. coli and Klebsiella pneumoniae revealed that most differences were clustered in four well defined regions. A PCR assay, based upon these variable sequences, allowed amplification of a fragment of gene fimA which is specific for most O2 strains. In addition, the sequence of the previously uncharacterised gene fimI, which is located between genes fimA and fimC, was determined.