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

Abstract

Copper has been used as a disinfectant since ancient times and recent research has demonstrated that 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 pH 7.0 was stored for up to 48 h in copper vessels at 5, 15, 25 and 35 degrees C. For pH, a bacterial suspension was stored at 30 degrees C 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 35 degrees C. These findings have important implications for the practical application of copper-based water disinfection methods, in terms of their likely efficacy under environmental conditions.

Inactivation and sub-lethal injury of Escherichia coli in a copper water storage vessel: effect of inorganic and organic constituents

“…This isolate was also used in our previous study (Sharan et al 2010), ensuring comparability with this research. The isolate was preserved by preparation of stocks following sub-culture on nutrient agar (HiMedia, Mumbai, India) at 37°C.…”

“…Copper vessels (capacity 12 l) were obtained from local merchants in Chandigarh, as before (Sharan et al 2010). Each vessel was filled with 10 l of bacterial suspension.…”

“…Similarly, inactivation of E. coli, Salmonella enterica serovar Typhi and Vibrio cholerae after overnight water storage in copper pots has been reported recently by Sudha et al (2009), based on conventional aerobic counts. Recent studies (Sharan et al 2010) have demonstrated the effect of temperature and pH on antibacterial action of copper against E. coli stored in pure water, with the observation that fastest inactivation took place at elevated temperatures and at pH furthest from neutrality. The present study was carried out to provide further information, by establishing the effects of water composition on this process.…”

“…Uninjured bacteria were enumerated under conventional aerobic conditions, while injured (ROS-sensitive) bacteria were enumerated under anaerobic conditions on a medium containing the peroxide scavenger sodium pyruvate, as in previous studies (e.g. Khaengraeng and Reed 2005;Tandon et al 2005;Sharan et al 2010).…”

Storing Drinking-water in Copper pots Kills Contaminating Diarrhoeagenic Bacteria

“…Copper pot is as active in regular drinking-water (pH 7.83±0.4) as that reported by us earlier (12) in distilled water (pH 6.7±0.05), and the level of copper leached in the former is far less (177±16 ppb) than that in distilled water (~420 ppb). Other studies have shown that copper vessel is lethal to E. coli in water at different pH and temperature conditions, with the fastest inactivation occurring as the pH shifts away from neutrality and 35 °C (15). Copper has also been shown to act, to a greater or lesser extent, on E. coli in the presence of organic and inorganic constituents in water (16).…”