Adhesion of clinical and environmental Aeromonas isolates to HEp-2 cells

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Abstract
A total of 63 Aeromonas strains isolated from diarrhoeal faeces or water samples were tested for adhesion to HEp-2 cells. An association between diarrhoea and high level adhesion was observed in that 12 of the 34 faecal isolates and none of the 29 environmental isolates yielded < 20 bacteria per HEp-2 cell in the adhesion assay. The proportion of high adherers was significantly greater for A. sobria (57%) than for A. hydrophila isolates (19%). Three of the eight faecal A. caviae isolates were also found to be high adherers. All of the environmental isolates were heavily pilated with pili having a mean diameter of 5 nm and a mean length of 420 nm; these were termed type-S pili. Of the 34 faecal isolates, 32% possessed S pili, and 68% were lightly pilated with up to 15 thin, flexible type-L pili, of mean diameter 2.5 nm and mean length 960 nm. Type-L pilation was associated with a high level of HEp-2 cell adhesion, and was more common in A. sobria and A. caviae than in A. hydrophila isolates. These results suggest that adherence to HEp-2 cells is a useful model for the investigation of Aeromonas enteropathogenicity, and that adhesion may be pilus-mediated in this organism.