INACTIVATION OF AEROMONAS-HYDROPHILA BY FE(II)-RELATED-RADICAL GENERATION IN OXIDIZING GROUNDWATERS

The survival of Aeromonas hydrophila AWWX1 in filter-sterilized phreat ic groundwaters was studied by using viable counts, Aeromonas counts r apidly decreased 2 to 3 log units in oxidizing raw groundwaters from S nellegem and Beernem, Belgium (Snellegem-raw and Beernem-raw, respecti vely), containing high concentrations of Fe2+ (460 to 1,070 mu M). The rapid decline in viable counts of Aeromonas cells in the oxidizing ra w groundwater of Snellegem was prevented by the addition of an Fe2+ ch elator (2,2'-dipyridyl) or compounds (i.e., ascorbic acid and catalase ) that act on toxic oxygen species. The results suggest that free radi cals, generated spontaneously in oxidizing Fe2+-containing groundwater s, caused the inactivation of A. hydrophila AWWX1, Evidence that free radicals are generated under the given conditions was provided by the observation that propylphosphonic acid, a compound which is very susce ptible to radicals, was degraded upon addition to these waters, A. hyd rophila PWBS, Pseudomonas fluorescens P17, Spirillum strain NOX, and h eterotrophs showed decreases in culturability in filter-sterilized Sne llegem-raw water similar to that shown by A. hydrophila AWWX1. These f indings indicate that free radicals generated in Fe2+-containing groun dwaters upon aeration are capable of inactivating various bacterial sp ecies.