Inactivation of Legionella pneumophila by combined systems of copper and silver ions and free chlorine.

The aim of this study was to evaluate the efficacy of copper and silver ions and of free chlorine in different combinations and concentrations (0.4 to 0.8-0.04 to 0.08 mg/l Cu(2+) Ag(+); 0.4 to 0.8-0.04 to 0.08-0.2 mg/l Cu(2+) Ag(+) Cl; 0.4 to 0.8-0.04 to 0.08-2 mg/l Cu(2+) Ag(+) Cl; 0.4 to 0.8-0.04 to 0.08-4 mg/l Cu(2+) Ag(+) Cl; 2-20 mg/l Cl), in inactivating Legionella pneumophila in drinking and distilled water after a contact time of 24-hours. Treatment with chlorine alone at 20 mg/l concentration was found to be the most effective treatment leading to complete killing of bacteria within 4 minutes in all water samples. On the other hand, at 2 mg/l concentration complete inactivation was obtained after 3 hours. The association of copper and silver ions at concentrations of 0.4-0.04 mg/l was found to be less effective and live bacteria could still be identified in all water samples after a 24 hour contact time. When testing copper and silver ions in combination, at concentrations of 0.8-0.08 mg/l and different combinations of the three disinfectants, results varied according to the various concentrations and type of water. The combination of copper and silver with 2 mg/l of chlorine was found to be more effective than 2mg/l of chlorine alone; a synergistic effect can therefore be hypothesized. The physical and chemical properties of drinking water, in particular its chlorine content, may have affected the water disinfection process when disinfecting agents were used in low concentrations. In conclusion, this study confirms the efficacy of shock hyperchlorination in the inactivation of Legionella pneumophila. However, the combination of free chlorine with metal (copper and silver) ions may represent a valid option for reducing the concentration of disinfectants to safer levels for human health and avoiding damage to water distribution systems especially in facilities such as hotels and hospitals.

Determination of the viability of Aeromonas hydrophila in different types of water by flow cytometry, and comparison with classical methods.

The presence of Aeromonas spp. in water can represent a risk for human health. Therefore, it is important to know the physiological status of these bacteria and their survival in the environment. We studied the behavior of a strain of Aeromonas hydrophila in river water, spring water, brackish water, mineral water, and chlorinated drinking water, which had different physical and chemical characteristics. The bacterial content was evaluated by spectrophotometric and plate count techniques. Flow cytometric determination of viability was carried out using a dual-staining technique that enabled us to distinguish viable bacteria from damaged and membrane-compromised bacteria. The traditional methods showed that the bacterial content was variable and dependent on the type of water. The results obtained from the plate count analysis correlated with the absorbance data. In contrast, the flow cytometric analysis results did not correlate with the results obtained by traditional methods; in fact, this technique showed that there were viable cells even when the optical density was low or no longer detectable and there was no plate count value. According to our results, flow cytometry is a suitable method for assessing the viability of bacteria in water samples. Furthermore, it permits fast detection of bacteria that are in a viable but nonculturable state, which are not detectable by conventional methods.