FAILURE to isolate Vibrio cholera from the faeces of patients with signs and symptoms of typical cholera is not an infrequent experience. Usually this is attributed to faulty laboratory techniques and, in spite of negative bacteriological findings, the cases are recorded as cholera. After careful investigation of some patients we were convinced that the faeces of a fair number of them yielded nothing but a pure culture of Bacterium coli. To determine their possible pathogenicity, we resorted to rabbit loop experiments which had been used by one of us (De and Chatterje, 1953) to study the action of V . choZera on the intestinal mucous membrane, and were surprised to find that many of these strains of Bact. coZi behaved in the same way as V . cholera. This led us to investigate whether the observed animal pathogenicity of strains of Bact. coli could be correlated with their biochemical, haemolytic and serological properties.
MATERIALS AND METHODSSpecimens of stool not more than two hours oldwere examined microscopically, and a loopful, or a flake of mucus when present, waa seeded upon plates of MacConkey's agar, desoxycholate citrate agar and taurocholate agar. Those samples which showed no ova or protozoa and no large number of pus cells and which yielded a pure or almost pure culture of Bact. coli but no V . cholerm or members of the shigelh group were used as sources of strains. A single isolated colony of Bact. coli from a plate culture of stool of each such case was subcultured on agar slopes for further study.Twenty strains were collected from twenty cases admitted with acute diarrhea with or without vomiting and with dehydration severe enough to require intravenous infusion of saline. Another twenty strains came from twenty ambulant persons who gave a histury of frequent attacks of diarrhoea following some indiscretion i n diet or habits. The last twenty strains were obtained from the faxes of healthy persons who c o r h e d that they never suffered from any bowel irregularity. I n addition to these sixty strains from adults, three strains belonging respectively to 0 groups 26, 55 and 11 1 isolated in England (Colindale) from caaes of acute infantile gastro-enteritis and kindly supplied by Dr Joan Taylor were included in the present investigation.All the strains were Gram-negative bacilli ; no attempt was made to demonstrate motility, which has been found to vary with many artificial factors * Present address :
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