Virulence characteristics of heterotrophic bacteria commonly isolated from potable water

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Abstract
Heterotrophic bacteria isolated from drinking water distribution systems were examined to determine if they possessed putative virulence factors such as hemolysins, proteases, or cytotoxins. Representative samples of colonies from several different distribution systems indicated that the median percentage of heterotrophic bacteria having at least one putative virulence characteristic was about 11% and all of the samples contained bacteria expressing at least one putative virulence characteristic. The overall frequency of bacteria from drinking water distribution samples expressing more than one putative virulence factor ranged from 0 to 8%. The eukaryotic cell culture cytotoxicity test appeared to be the most reliable indicator of those bacteria expressing multiple virulence factors. The results also indicated that the expression of putative virulence factors was highly dependent upon the type of isolation medium used. Although slow‐growing heterotrophic bacteria occurred at high densities in certain systems, they expressed very few of the putative virulence factors observed in this study. © 1993 John Wiley & Sons, Inc.