Comparative study of expression of hemagglutinins, hemolysins, and enterotoxins by clinical and environmental isolates of non-O1 Vibrio cholerae in relation to their enteropathogenicity

Abstract

A comparative study was undertaken of clinical and environmental isolates of non-O1 Vibrio cholerae with respect to their hemagglutinating, hemolytic, enterotoxigenic, and enteropathogenic activities. Cell-associated hemagglutinin titers of the clinical and environmental isolates did not differ much, although the clinical isolates displayed higher cell-free hemagglutinin titers compared with those of environmental isolates. Culture supernatants of 61.5% (24 of 39) of clinical isolates showed hemolytic activity (greater than or equal to 10% lysis of rabbit erythrocytes), while only 33.3% (10 to 30) of the environmental group had such activity. Furthermore, hemolytic activities of the clinical isolates showed a good correlation with their cell-associated hemagglutinin titers which was not true for the environmental group. Culture supernatants of 45.8% (11 of 25) of the clinical and 20% (2 of 10) of the environmental isolates exhibited enterotoxigenic activity in the rabbit ileal loop assay. Such activity was mediated mainly by cholera toxin-like substances, although some of the isolates produced fluid-accumulating factors unrelated to cholera toxin. Experimental animal studies demonstrated that the enteropathogenic potential of the environmental isolates was significantly lower than that of the clinical group. Further analysis of our data showed that phenotypic expression of cholera toxin-like products by the non-O1 V. cholerae isolates was accompanied by their enteropathogenicity. The latter effect was also noted with some of the cholera toxin-negative isolates, particularly in those having high hemagglutinating and hemolytic titers.