Characterisation of potential virulence markers in Aeromonas caviae isolated from polluted and unpolluted aquatic environments in Morocco

A total of 100 Aeromonas caviae strains isolated from river waters (38 isolates), raw sewage (30 isolates) and effluents of stabilisation ponds (i.e. treated sewage; 32 isolates) in Marrakech, Morocco, were tested for the presence of putative virulence factors to delineate differences, if any, in their enteropathogenic potential in relation to the source of isolation. A number of A. caviae isolates were able to elaborate at least one of the tested virulence factors. Of the 100 strains tested, 27 were capable of producing haemolysins, 19 produced cytotoxin, 24 produced cytotonic toxin, while 18 of the isolates possessed the capacity to adhere to HenLe 407 human intestinal cells with more than five bacteria adhering per cell. In order to assess the virulence potential of A. caviae isolates in relation to the source of isolation, we suggest the potential virulence index (PVI) as a tool for comparison. It is calculated as PVI = x/ny, where x is the number of positive occurrence of virulence factors in a population y, and n is the number of suitable virulence factors used for the calculation of the PVI. Accordingly, in this study A. caviae strains isolated from treated sewage samples showed a higher PVI (= 0.406) than those isolated from raw sewage (PVI = 0.175) or those from river waters (PVI = 0.09). These results suggest that stabilisation pond systems used for sewage purification under arid climate conditions in Marrakech, may have selected potentially enteropathogenic A. caviae strains. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.