Prevalence of the genes for shigella enterotoxins 1 and 2 among clinical isolates of shigella in Israel

Abstract

Two enterotoxins, shigella enterotoxin 1 (SHET1) and shigella enterotoxin 2 (SHET2) have been recently characterized and are believed to play a role in the clinical manifestation of shigellosis. One hundred and twenty-one isolates of Shigella spp. of 13 different serotypes and variants and 10 isolates of enteroinvasive Escherichia coli (EIEC) isolated in Israel, were examined by polymerase chain reaction for the presence of SHET1 and SHET2 genes. SHET1 was only prevalent among isolates of S. flexneri 2a while SHET2 was found in all the serotypes that were tested except for several isolates of S. flexneri 1b that lost their virulence plasmid during storage. In addition, we found that the S. flexneri 2a vaccine strain T-32 Istrati contains the gene encoding for SHET1 but not that encoding for SHET2, suggesting that the latter is located within a large deletion occurring in the 140 Mda plasmid of this S. flexneri 2a non-invasive vaccine strain.