RESISTANCE OF BACTERIAL CULTURES TO NONOXIDIZING WATER-TREATMENT BACTERICIDES BY ADAPTATION

Bacterial communities in water cooling systems treated with bactericid es often become resistant to these bactericides. This has been ascribe d to selection for resistant cells. Certain bacteria, having a high in herent susceptibility to water treatment bactericides become dominant in systems after bactericide treatment. We investigated the idea that bacterial isolates adapt to grow in the presence of bactericides. Pure cultures of Pseudomonas aeruginosa, P stutzeri and Bacillus cereus we re cultured repeatedly in the presence of subinhibitory concentrations of 2,2'-methylenebis(4-chlorophenol), Na dimethyldithiocarbamate, iso thiazolone and alkyl dimethyl ammonium chloride. All isolates adapted to grow in the presence of increasing concentrations of the bactericid es. The phenomenon of development of bacterial resistance to water tre atment bactericides was ascribed to adaptation and not to selection.