著者

涌嶋 三津子 王 麗麗 日高 あゆみ 藤原 佐美 中島 涼 石 娟娟 西川 禎一

出版者

Osaka Urban Living and Health Association

雑誌

生活衛生 (ISSN:05824176)

巻号頁・発行日

vol.54, no.4, pp.271-284, 2010-10-30 (Released:2010-11-10)

参考文献数

57

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Escherichia coli is a normal inhabitant of the intestinal tract in humans and warm-blooded animals; however, certain strains cause enteric disease in their hosts and are referred to as diarrheagenic E. coli (DEC). Based on distinct epidemiological and clinical features, specific virulence determinants, and other characteristic markers such as enterotoxins and adherence phenotype, DEC strains have been classified into the following six pathotypes: enteropathogenic E. coli; Shiga toxin-producing E. coli; enterotoxigenic E. coli (ETEC); enteroinvasive E. coli; enteroaggregative E. coli (EAEC); and diffusely adhering E. coli. E. coli that does not have any diarrheagenic characteristics other than the EAEC heat-stable toxin 1 (EAST1) gene is defined as EASTEC. Although EAST1 has not been widely accepted as a virulence factor, we focused our attention on EASTEC because outbreaks due to EASTEC O166:H15 have occurred in several cities since the first incident in Osaka, Japan, in 1996. In the present review, we discuss EASTEC as a possible seventh group of DEC. Guanylin is secreted in the colon and acts physiologically as an agonist of the guanylyl cyclase receptor to regulate electrolyte and water transport in the epithelia. EAST1, like the heat-stable enterotoxins of ETEC, may mimic guanylin and cause diarrhea. However, epidemiological studies show that the EAST1 gene (astA) is very prevalent not only among EASTEC strains from diarrheal patients but also in healthy people, domestic animals, and meat products. The presence of astA itself may therefore not necessarily indicate that the strain will be diarrheagenic in the intestine. Production of active EAST1 should be checked since astA seems to have numerous variants. The development of a convenient assay for EAST1 is essential. Further epidemiological studies are also required to elucidate whether EASTEC forms a seventh group of DEC; such studies would also identify additional virulence traits such as colonization factor.