Effects of culture conditions and biofilm formation on the iodine susceptibility of legionella pneumophila

Abstract

Alternatives to chlorination of water have been sought for reasons which include trihalomethane formation, possible bacterial regrowth, the high concentrations of chlorine required in certain circumstances, and the taste, odour and bodily irritation in chlorine-treated water. Electrolytically generated Cu and Ag ions at low levels, in addition to very low chlorine concentrations, have been suggested as an alternative to routine chlorination. We have examined the combination of Cu and Ag ions with low levels of iodine. Pseudomonas cepacia was grown either in rich medium or under nutrient restriction prior to disinfection. Survival of the organism and its ability to regrow after treatment as well as the effects of varying buffers, metal ion and iodine concentrations were determined. Low concentrations of metal ions (100 ppb Cu and 11 ppb Ag) and iodine (200 ppb) were more effective than either metal ions or iodine alone against Ps. cepacia grown on rich agar or in low nutrient buffer. After iodination, buffer-grown suspensions recovered to their original cell concentrations within 7 d. When Cu and Ag ions were used with or without iodine, regrowth was prevented. The results show that low concentrations of Cu and Ag in combination with iodine permit effective disinfection of bacteria after cultivation on either rich media or under nutrient restriction. These results, along with published data, suggest that the combination of these metals with halogenation may have applications in the disinfection of both recreational and potable water.