Diarrhea due to Escherichia coli in the rabbit: a novel mechanism

A strain of Escherichia coli 015 (RDEC-I) isolated from several rabbits with diar-rhea was examined to determine (1) whether the strain could produce diarrhea when administered by the orogastric route to other rabbits and (2) whether this strain was invasive or enterotoxigenic. Strain RDEC-I produced diarrhea in 48 of 62 rabbits when given by the orogastric route in doses that ranged from 1.5 X 102 to 4 X 1010 bacteria. The organism did not give a positive result in the I8-hr ileal loop or Sereny tests and did not invade HeLa cells. Culture supernatants of strain RDEC-I did not give positive results in the 6- or IS-hr rabbit ileal loop, suckling mouse, V-I adrenal cell, or Chinese hamster ovary cell assays. Fluorescent antibody staining of sections of intestine prepared in a cryostat revealed great numbers of E. coli strain RDEC-I that adhered to the epithelial surface. It is evident that E. coli can produce diarrhea without being able to invade the mucosa or synthesize enterotoxin. Strains of E. coli similar to RDEC-I may account for some of the E. coli-associated diarrhea that occurs in humans. Escherichia coli have been shown to cause diar-rhea by invasion of the intestinal mucosa or by synthesis of heat-labile or heat-stable entero-toxins [1-4]. Recent epidemiologic studies of diarrhea in human populations have utilized a number of different assays for determination of whether E. coli isolated from patients wi th diarrhea possess the ability to invade the intes-tinal mucosa or to synthesize enterotoxins. In-variably, E. coli cultured from a percentage of patients in each study lacked these capabilities, and it was concluded that the diarrhea had some other cause [2, 5-11]. It may be that some strains of E. coli associated with diarrhea in humans lack recognized pathogenic mechanisms and pro-duce diarrhea by a mechanism similar to that of the E. coli described herein. Received for publication June 1, 1976, and in revise