Temperature Stress Affects Survival and Antibiotic Susceptibility of Pathogenic and Indicator Bacteria in Drinking Water Dispensing System

Point-of-use water treatment and dispensing systems are becoming common features in middle-to-upper class homes and public spaces. However, their effectiveness at providing potable water is yet to be substantiated. In this study, the effect of temperature stress (cold ≈ 10oC and hot ≈ 78oC) on survival of three pathogenic (Salmonella typhi, Shigella dysenteriae, Vibrio cholerae), a nuisance (Proteus vulgaris) and the indicator (Escherichia coli) bacteria was evaluated in water dispensers. Individual test organism was spiked into pre-sterilized distilled water in a 25-L dispenser bottle. The bottle was fitted and the machine set on to allow the organisms acclimatized for 30 mins before samples were collected. The holding temperatures apparently had an immediate significant inhibitory effect (p<0.05) on the pathogens, being greater in dispensed hot water. Effect of cold temperature stress was least on Escherichia coli. While Shigella dysenteriae and Vibrio cholerae were completely inactivated in dispensed hot water, there were some levels of resuscitation in the other organisms that were initially stressed by either the hot or cold temperature after just 1 h of cooling to room temperature. The re-inactivation was significant (p<0.05) in the dispensed cold water for Salmonella typhi and Vibrio cholerae. With exception of Shigella dysenteriae, other organisms exhibited varied susceptibility (5–11 mm) to six of eight antibiotics; this appeared to increase following the temperature stress. However, increased resistance to augmentin, nitrofurantoin and tetracycline was observed in some temperature-stressed strains, particularly Salmonella typhi and Vibrio cholerae as well as Escherichia coli. The findings indicate that, while hot or cold temperature may have an immediate inhibitory effect on microbial loads and antibiotic susceptibility, the unwholesome practice of drinking dispensed water several hours after should be discouraged.