Differentiation of Shiga toxin and Vero cytotoxin type 1 genes by polymerase chain reaction

Two sets of synthetic oligonucleotide primers were used in a polymerase chain reaction technique to distinguish genes for Shiga toxin in Shigella dysenteriae 1 and type 1 Vero cytotoxin (VT1) in Escherichia coli. VT1a and VT1b primers directed at a common 130-base-pair (bp) fragment of the stx and sltI genes detected template nucleic acid in both Shiga toxin-positive S. dysenteriae 1 and VT1-producing E. coli strains. VT1c and VT1d primers, targeting a 140-bp fragment of the promoter region of the sltIA gene, were negative in the polymerase chain reaction with S. dysenteriae 1 nucleic acid and positive with nucleic acids from all strains found to produce VT1 in toxin-specific neutralization tests. Primer specificity was determined in the polymerase chain reaction using nucleic acid extracted from 49 strains of representative enteric pathogens defined in terms of their toxigenicity.