Aquucutture, 67 (1987) 29-39 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFED Elsevier Science ~blishe~ B.V., Amsterdam - Printed in The Netherlands 29 zyxwvuts Relationships Among Virulence for Fish, Enterotoxigenicity, and Phenotypic Characteristics of Motile zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQP Aeromonus YSABEL SANTOS*, ALICIA E. TORANZO, CARLOS P. DOPAZO, TERESA P. NIETO and JUAN L. BARJA ~e~artamento de Microbiology y ~ar~ito~gio, F~cult~d de ~io~og~~, Uniuersid~d de Santiago de Compostela, Santiago 15703 <Spain,I “To whom correspondence should be addressed. (Accepted 22 January 1987) ABSTRACT Santos, Y., Toranzo, A.E., Dopazo, C.P., Nieto, T.P. and Barja, J.L., 1987. Relationships among virulence for fish, enterotoxigenicity, and phenotypic characteristics of motile Aeromonas. Aquaculture, 67: 29-39. In this study we have analysed the biochemical, enzymatic, and cell surface properties of 59 Aeromonas strains isolated from fish culture systems, with the aim of establishing the possible relationships among some of these phenotypic characters and pathogenicity. The cytotoxic activ- ity of extracellular products was also evaluated. Virulence assays showed that 64.3% of the strains were pathogenic for fish. However, both pathogenic and non-pathogenic Aeromonas isolates were able to produce enterotoxins. The ma- jority of the strains were proteolytic, amylolytic and produced DNAase. Nevertheless, elastase and staphylolytic activities were present only in A. hydrophilu. Although 96% of the isolates produced haemolysins, a clear specificity toward trout or human erythrocytes was not found in the patho- genic strains. Similarly there was no specificity in the haemagglutinating activity. Statistical analysis of the association between virulence and phenotypic traits revealed a posi- tive relationship among virulence for fish and arabinose and sucrose fermentation, elastase and haemolysis of human erythrocytes. However, only the LDC test showed a significant relation with enterotoxin production. These findings suggest that different mechanisms are involved in the invasion by Aeromonas of their poikiIotherm and homeotherm hosts. Extracellular products of the Aeromonas strains displayed cytotoxicity on fish cell-lines regard- less of the virulence capacities of the strains, which indicates that cytotoxic activity is not an adequate criterion of pathogenicity. INTRODUCTION Motile zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Aeromonm are considered autochthonous inhabitants of aquatic en- vironments and have been documented as opportunistic pathogens for fresh- OOZE-8~86/87/$03.50 0 1987 Elsevier Science Publishers B.V.