Inactivation and injury of Escherichia coli in a copper water storage vessel : effects of temperature and pH

Copper has been used as a disinfectant since ancient times and recent research has demonstrated those antimicrobial copper surfaces may have practical applications in healthcare and related areas. The present study was carried out to establish the effects of temperature and pH on inactivation and sub-lethal injury of Escherichia coli in water stored in a copper vessel, to determine the operational limits of the process in terms of these variables. To investigate the effects of temperature, a bacterial suspension at pH7.0 was stored for up to 48 h in copper vessels at 5, 15, 25 and 35C. For pH, a bacterial suspension was stored at 30C for up to 48 h in copper vessels at pH 6.0, 7.0, 8.0 and 9.0. Both temperature and pH had substantial effects on inactivation and injury, with the fastest inactivation observed at elevated temperature and at pH values furthest from neutrality, while the greatest amount of sub-lethal injury, manifest as sensitivity to conventional aerobic enumeration, was observed at a temperature of 35C. These findings have important implications for the practical application of copper basedwater disinfection methods, in terms of theirlikely efficacy under environmental conditions.