Outbreaks of Acute Enteritis Due to Heat‐Stable Enterotoxin‐Producing Strains of Escherichia coli

(ST). The pathogenic action of LT in causing diarrhea has been intensively investigated in comparison with that of cholera enterotoxin (2, 4, 8), and has been shown to be quite similar to the action of the latter in terms of adenyl cyclase stimulating effects (3). On the other hand, the mode of action of ST in developing diarrhea is still obscure. Although ST-only-producing E. coli has been considered for a long time as a cause of animal diarrhea (7), Sack et al (5) recently reported the successful isolation of such E. coli from three travelers' diarrhea specimens in Meixco City. During the past 8 years, there have been 38 outbreaks of E. coli enteritis consisting of 2,315 patients in Tokyo. At first, we attempted to test enterotoxin productivity of the isolates which did not belong to the enteropathogenic E. coli in the classical sense but were presumed to be the only pathogen in the outbreaks. It was found that five outbreaks were due to E. coli O6 .H16 producing both LT and ST, and seven were due to ST-only-producing strains. This paper describes the delineation of enterotoxin production of the isolates which produced ST without producing LT, and the epidemiological aspects of the outbreaks due to them. The enteropathogenicity of isolates was examined by three currently recognized. models : Chinese hamster ovary (CHO) cell tissue culture assay, intragastric inoculation in infant mice and Sereny's test. For testing LT, a modified method of the CHO cell assay was adopted in which the action of the toxin was detected by observing a change in the morphological appearance of colonies, instead of the ordinary method of observing the elongation of individual cells. When cultured CHO cell colonies were incubated with a dilution ranging from one tenth to one hundredth of an original culture filtrate of LT-producing E. coli, the smooth round colonies showed a shape resembling a chrysanthemum in appearance after 18 to 24 hr of incubation, which was due to the elongation of individual cells in the colonies. When a change of greater than 5% in counting 100 colonies occurred, it was considered that the test sample contained LT. For the assay of ST, 0.1 ml of a culture filtrate heated at