V. cholerae. A mannose-sensitive lectin-like adhesin produced by motile Aeromonas strains was shown to coagglutinate with some Salmonellae 3 Whether this can be of importance in the course of Aeromonasor Salmonella-associated intestinal infections remains to be investigated. Strains of Aeromonas were found to adhere to rabbit brush border cells and rabbit intestines in low numbers 14, whereas human Aeromonas isolates adhered in high numbers to isolated human intestinal cells (M. Lindahl, ,~. Ljungh, unpublished). Furthermore, human and animal Aeromonas isolates commonly express pronounced surface hydrophobicity in contrast to strains isolated from water and shellfish which are often surrounded by a slimy, hydrophilic material. In summary, Aeromonas strains produce surface proteins of fimbrial and non-fimbrial nature which can represent surface adhesins with different host specificity in analogy to the plethora of E. coli adhesins. They can also be involved in determining the level of adhesion in the gut. Conclusions The role of fl-hemolysin in soft tissue infection is well established. In diarrheal disease, however, correlation to biotype is circumstantial and no correlation between presumptive virulence factor and infection has been shown. In animal feeding experiments as well as in human volunteer studies Aeromonas strains with defined characteristics failed to induce diarrhea 16,19, 20. Aeromonas intestinal infection may present as 1) toxigenic, ricewater, small intestinal diarrhea, 2) classical dysentery involving the large intestine, or as 3) combinations of the two extremes. It is likely that surface characteristics determine the level of adhesion and that the production of toxins and enzymes determines the severity of disease. Certain combinations of toxins, enzymes and surface factors are probably crucial for establishing infection. To study this, wild type strains and a panel of mutants devoid of selected virulence factors must be characterized and tested in appropriate models.