Cloning, DNA nucleotide sequence and distribution of the gene encoding the SEF14 fimbrial antigen of Salmonella entevitidis

Abstract

Monoclonal antibody 69/25, specific for the Salmonella enteritidis fimbrial antigen (SEF14), was used to screen a pUC-based S. enteritidis gene library and a positive clone was identified. Subcloning experiments demonstrated that a 584 bp DraI DNA fragment was the minimal chromosomal segment capable of directing SEF14 antigen expression. Western blotting of Escherichia coli recombinants identified a gene product of M(r) 16000 as a precursor to the M(r) 14300 mature fimbrial subunit protein. The DNA nucleotide sequence of the DraI fragment was determined and was shown to contain a single open reading frame with two potential f-Met start codons and a hydrophobic signal sequence. Downstream of a putative peptidase cleavage site, the deduced amino acid sequence showed considerable homology with the N-terminal amino acid sequence of what was originally described as the type 1 fimbrial subunit of Salmonella enteritidis and later redefined as SEF14. The gene encoding SEF14, designated as sefA, was shown to be limited in distribution to Salmonella blegdam, S. dublin, S. enteritidis, S. gallinarum, S. moscow, S. pullorum, S. rostock, S. seremban and S. typhi, all belonging to Salmonella group D. However, expression of the SEF14 antigen was limited to S. dublin, S. enteritidis, S. moscow and S. blegdam. The nucleotide sequence of the sefA gene shared no homology with the Salmonella fimA gene encoding type 1 fimbriae, and these genes showed distinct patterns of distribution within salmonellae.