Cloning and nucleotide sequence of a variant Shiga-like toxin II gene from Escherichia coli OX3:H21 isolated from a case of sudden infant death syndrome.

Escherichia coli OX3:H21 expressing a toxin related to Shiga-like toxin (SLT) was isolated from the small bowel contents of a case of Sudden Infant Death Syndrome (SIDS). This strain was lysogenic for a lambdoid bacteriophage, but this did not encode the toxin. Southern hybridization analysis of chromosomal DNA revealed that the SLT-related gene was located on a 4.6 kb PstI fragment, which was cloned into E. coli JM109 in both orientations, using the vector pUC19, to generate plasmids pJCP501 and pJCP502. JM109 cells harbouring the recombinant plasmid produced SLT, as judged by cytotoxicity for Vero cells. Nucleotide sequence analysis revealed that the SLT gene was related to, but distinct from, previously reported variants of Shiga-like toxin type II, produced by E. coli from both human and animal sources. The A subunit of the SLT gene from OX3:H21 exhibited 95.9% homology (at both the DNA and derived amino acid sequence level) to the A subunit of the most closely related SLT-II variant. The B subunit was less similar, exhibiting 88.6 and 88.8% homology to the related gene at the DNA and amino acid level, respectively.