Enterotoxin-associated DNA sequence homology between Salmonella species and Escherichia coli

Multiple Hin</it>dIII-restriction fragments of Salmonella typhimurium</it> and Salmonella typhi</it> chromosomal DNA exhibited homology with the heat-labile enterotoxin (LT1) gene of Escherichia coli</it> as determined by Southern blot analysis. A 9.4 kb Hin</it>dIII restriction fragment identified in S. typhimurium</it> and S. typhi</it> chromosomal DNA reacted with both eltA</it> and eltB</it> gene probes. However, the homology of the 9.4 kb DNA fragment from these Salmonella</it> species was greater with eltB</it> than eltA</it>. In addition, a synthetic oligonucleotide probe, made to a portion of the putative G<inf>M1</inf>-ganglioside binding region of cholera toxin (CT) and LT1, hybridized with the 9.4 kb DNA fragment of S. typhimurium</it> but not with the 9.4 kb fragment found in S. typhi</it> isolates. The hybridization of multiple restriction fragments of Salmonella</it> DNA with eltA</it> and eltB</it> gene sequences further suggests duplication of the stx</it> operon on the chromosome of these bacteria.