Haemagglutinating activity, serum sensitivity and enterotoxigenicity of Aeromonas spp

Of 97 isolates of Aeromonas 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 A. hydrophila than of A. sobria or A. caviae. 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 A. caviae (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.