SUMMARY Over a four and a half month period, 1004 unselected routine faecal specimens from 815 patients were cultured for Aeromonas hydrophila. Forty-two specimens (4.2%) representing 38 patients were culture-positive. The study specimens also yielded Salmonella on 116 occasions, Shigella on seven, Campylobacter species on six and other bacterial pathogens on 17 occasions respectively. Seven specimens had A hydrophila together with another bacterial pathogen. In only 19 of 38 patients (50%) was A hydrophila possibly associated with gastrointestinal symptoms. All the Aeromonas isolates were resistant to ampicillin but sensitive to gentamicin, piperacillin, mecillinam, chloramphenicol, ceftazidime and colistin.
Summary. Ninety-five strains of Aeromonas were divided into three species-A. sobria, A . hydrophila and A . caviae-on the basis of results in 13 biochemical tests. The minimum number of tests necessary to distinguish these species was determined. Culture filtrates of the strains were tested for cytotoxin and cytotonin, haemolysin and protease. One filtrate with high-titre cytotoxin, haemolysin and protease activities was subjected to gel filtration on Sephadex G75 and isoelectric focussing. Of the five cell lines tested, Vero cells were most sensitive to the cytotoxin; no reproducible cytotonic effects were observed. The haemolysin effect appeared to be equivalent to cytotoxin. At least two distinct protease activities were found that might be responsible for the cytotonic effects described. Cytotoxin production was species related; it was present in A. sobria and A. hydrophila but not in A . caviae.
Summary.One hundred and eleven isolates of Aeromonas from water and from human sources were identified to species level and tested for the production of cytotoxin. These results were correlated with the source of each isolate and, for those from human faeces, with the clinical history of diarrhoea. A. caviae predominated in water, comprising 16 of 32 isolates; only one isolate from water was A. sobria. In human faecal samples 21 of 76 isolates were A. sobria; this was a significant difference. Cytotoxin producing strains were significantly more common in patients with no known cause for their gut symptoms. It is concluded that gastro-enteritis caused by Aeromonas is related to species and to production of cytotoxin.
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