Of 97 isolates of spp. that were examined for haemagglutination (HA) and enterotoxigenicity, 35 were from clinical and 62 from environmental sources; 66 of them were also screened for sensitivity to normal human serum (NHS). HA was caused by 44 isolates (45%); it was unrelated to the source of the strain, but it was caused by a higher proportion of the isolates of than of or . Of the haemagglutinating strains, 82% were enterotoxigenic, whereas most of the non-haemagglutinating strains were non-toxigenic when tested initially. All the latter became enterotoxin producers after serial passage through rabbit ileal loops, but without change in HA. Most (64%) of the isolates, including 68% of (72% of clinical and 65% of environmental), were resistant to the bactericidal action of NHS. Most (92%) of the serum-sensitive strains were killed by activation of both the classical and alternate pathways of complement, the others only by the alternate pathway. Most (74%) of the serum-resistant strains caused fluid accumulation in the initial tests in ileal loops, regardless of species or source. Haemagglutinating and serum-resistant strains caused significantly more accumulation of fluid (p≪0·05) than non-haemagglutinating and serum-sensitive strains. This study shows partial correlation between HA or serum sensitivity and enterotoxigenicity, but the properties are probably not genetically linked.


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