Production of Shiga-Like Toxin by Escherichia coli

Abstract

Production of Shiga-Like Toxin by Escherichia coli Escherichia coli is one of several agents that cause intestinal disease in humans and animals. Four classes of E. coli have been recognized [1], Enterotoxigenic E. coli (ETEC) strains produce a heat-labile (LT) enterotoxin and/or a heat-stable (ST) enterotoxin. Enteroinvasive E. coli (EIEC) strains, like shigellae, penetrate and multiply within epithelial cells. Enteropathogenic E. coli (EPEC) strains belong to certain serogroups that have been incriminated as pathogens by epidemiological studies. Some EPEC strains have been shown to adhere to cells of the intestinal mucosa and to produce pathognomonic lesions at the site of attachment. Enterohemorrhagic E. coli (EHEC) strains cause a distinct clinical syndrome (hemorrhagic colitis), and serotype 0157:H7 has been associated with this illness. Neither EPEC nor EHEC strains produce classic enterotoxins, nor are they enteroinvasive. Some strains of E. coli produce a cell-associated cytotoxin that is neutralized by antibodies against purified Shiga toxin from Shigella dysenteriae type 1 [2-4]. The cytotoxins purified from one EPEC strain 026:H11 (H30) and from one EHEC strain 0157:H7 (933) have biologic activities (cytotoxicity for HeLa and Vero cells, lethality for mice, and enterotoxicity for ligated ileal segments from rabbits) and subunit structures similar to those of Shiga toxin [5, 6]. The purpose of this study was to determine the frequency and levels of cytotoxin production for a wide variety of E. coli strains. Culture supernatants and sonic lysates of 418 strains isolated from humans, animals, ajid food were examined for cytotoxic effects on HeLa cells and to see whether cytotoxicity could be neutralized by antibodies to Shiga toxin. Materials and Methods Bacterial strains. E. coli strains examined for production of Shiga-like toxin were obtained mainly from the Centers for Disease Control, Atlanta, Georgia. The 418 strains were isolated over a period of 30 years from the following: humans with diarrhea, hemorrhagic colitis, hemolytic uremic syndrome, or no clinical manifestation of disease; calves with diarrhea; piglets with edema dis

Transcription of the Shiga-like toxin type II and Shiga-like toxin type II variant operons of Escherichia coli

“…Microcytotoxicity assays were done on HeLa and Vero cells according to published modifications (27) of the methods of Gentry and Dalrymple (14). The last dilution of the sample in which greater than or equal to 50% of the HeLa or Vero cells detached from the plastic as assessed by A620 measurements was considered the 50% cytotoxic dose (CD50).…”

Virulence factors of enteropathogenic Escherichia coli

“…Another study revealed that 59% of strains from outbreaks of diarrhoea were SDT producers. Some strains of E. coli, however, that gave negative results when cell sonicates were used, gave positive results when French-press lysates were tested (Marques et al, 1986). Whether all EPEC strains produce SDT to some extent, and whether the inability to detect it results from a lack of sensitivity in the assay system, remains to be determined.…”

“…Diarrhoea caused by EAEC strains is generally less severe than that caused by EPEC strains. As some EPEC strains do not produce detectable Shiga toxin (Marques et al, 1986), they may in fact resemble EAEC strains. It should be noted, furthermore, that HEp2 adhesion in EAEC is distinct from that of EPEC strains (Levine, 1987).…”

Roles of a ribosome-binding site and mRNA secondary structure in differential expression of Shiga toxin genes

“…Therefore, we propose that independent translation of the slt-IL4 and slt-IIB genes is the sole factor governing the stoichiometry of SLT-II subunit production. Perhaps this explains why the level of SLT-II produced in vitro is significantly lower than that of STX (24).…”