Hafnia alvei, a probable cause of diarrhea in humans.

Hafnia alvei, a member of the family Enterobacteriaceae, was the only species of bacteria cultured from the stool of a 9-month-old child who was admitted with a 3-day history of watery diarrhea. The isolated strain of H. alvei failed to produce heat-labile or heat-stable enterotoxins or Shiga-like toxin I or II and did not invade HeLa cells, nor did it cause keratoconjunctivitis (determined by the Sereny test) in a guinea pig's eye. The strain, however, induced diarrhea in 8 of 12 adult rabbits with removable intestinal ties (removable intestinal tie-adult rabbit diarrhea [RITARD] assay) and in 1 of 2 orally fed animals. No diarrhea could be induced with Escherichia coli K-12 in eight RITARD assay rabbits and three orally fed rabbits, respectively. Microscopic examination of affected animals revealed moderate inflammatory cellular infiltration of the intestinal mucosa, in which bacterial attachment to the surface epithelium and loss of the microvillus border were evident in the ileum and colon. Electron microscopy demonstrated cellular modifications of the apical surface, with cupping or pedestal formation and increased terminal web density at sites of bacterial "attachment-effacement," a well-known characteristic and mechanism of diarrhea of enteropathogenic E. coli. Identical lesions were also induced by H. alvei in rabbit ileal loops, which ruled out naturally occurring rabbit enteropathogenic E. coli strains, which are known to produce similar lesions. It is concluded that at least some strains of H. alvei have the potential to cause diarrhea and that attachment-effacement is a virulence characteristic shared by bacteria other than E. coli.

Experimental studies on the pathogenicity of Vibrio mimicus strains isolated in Bangladesh.

Vibrio mimicus, a newly described species of the genus Vibrio has been isolated from stools of 14 patients with diarrhoea. Live cells of all the 14 strains tested caused accumulation of fluid in rabbit gut loops and diarrhoea in infant rabbits. Culture filtrates of all the strains caused increased capillary permeability in rabbit skin; however, five of the filtrates resembled cholera toxin in that they gave positive reactions in rabbit loops, chinese hamster ovarian and mouse adrenal cell monolayers and GM1 ELISA tests and were neutralized by cholera antitoxin. None of the strains produced heat-stable toxin or possessed invasive capability as determined by Sereny's test. Thus, V. mimicus strains were divided into a group which produced a toxin immunobiologically similar to cholera toxin and the rest producing a heat-labile toxin unrelated to that of V. cholerae.