Escherichia Coli O157 H7 and Shiga-like-toxin- producing Escherichia Coli in China.

Abstract

Escherichia coli (E. coli) is one of the facultative anaerobes of the human intestinal tract, usually harmless. Infections due to pathogenic E.coli may result in urinary tract infections, sepsis, meningitis and enteric disease. Diarrheagenic E.coli has been classified into several categories, such as enterotoxigenic E.coli (ETEC), entero-invasive E.coli (EIEC), entero-pathogenic E.coli (EPEC), enteroaggregative E.coli (EaggEC) and entero-hemorrhagic E.coli (EHEC). A variety of virulence or potential virulence factors for diarrheagenic E.coli have been identified. The nomenclature of diarrheagenic E.coli is based on virulence factors. In 1977 Konowalchuk et al reported that some strains of pathogenic E.coli O26 : H11 produced a toxin with a profound cytopathic effect on Vero cells, and named it verotoxin (VT). O’Brien et al noted that the VT reported by Konowalchuk et al was strikingly similar to Shiga toxin (Stx) produced by-Shigella dysenteriae type 1, and it could be neutralized by antiStx, thus a new nomenclature, Shiga-like toxin (SLT), appeared. An alternative nomenclature is “Shiga toxin” (ST), which indicated t hat the specific cytotoxin described by Konowalchuk et al is esse ntially identical at the genetic and protein levels with the Stx produced by S. dysenteriae I discovered some 100 years ago. Consequently, SLT, ST and VT have been used interchangeably, resulting in the name of verotoxinproducing E.coli (VTEC), shiga-like-toxinproducing E.coli (SLTEC) and shiga-toxin-producing E.coli (STEC) coexisted in literature. However, it must be noted that E.coli O157 : H7 is the main serotype of EHEC recognized at present. Hemorrhagiccolitis (HC) and hemolytic uremic syndrome (HUS) are life threatening, which are often caused by STEC or EHEC. So far as the diseases are concerned, E.coli O157 : H7 should belong to EHEC. All of the EHEC strains are believed to be pathogenic. As for its toxin, E.coli O157 : H7 should belong to VTEC, SLTEC or STEC. However, not all of the STEC strains could cause HC or HUS. The confusion from the nomenclature may be clarified in future when the pathogenic mechanisms of bacteria are fully understood. Food-borne outbreaks of SLTEC disease appear to be increasing in the world. Mass-produced and mass-distributed food can involve large numbers of people in short time. SLTEC strains belong to a very diverse range of serotypes, among which O157 : H7 is most commonly associated with large outbreaks. In the summer of 1996 in Japan, a largest outbreak in the world caused by E.coli O157 : H7 was reported, in which about 10 000 cases were identified. Chinese grovernment and society became aware of the importance of E.coli O157 : H7 from the Japanese outbreak. An informal national network for detection of E.coli O157 : H7 was organized in April 1997, involving about 30 public health laboratories from different provinces and municipalities.