Prevalence of free-living acanthamoeba and its associated bacteria in energy-efficient hot water systems in South Africa

As part of the Eskom rebate programme, energy-efficient hot water systems such as solar water heaters (low pressure), heat pumps and energy-efficient showerheads were rolled out to the public as a measure to conserve and save energy.  There has been a concern that these systems may not reach the required high temperatures, especially during winter, and, as a result of this, Acanthamoeba and its associated bacteria such as Legionella pneumophila, Pseudomonas aeruginosa and nontuberculous mycobacteria could flourish within these systems causing a potential health risk to consumers.  This study examined the relationship between Acanthamoeba and its associated bacteria at different temperature ranges. A total of 156 water (69) and biofilm samples (87) were collected from a solar water heater, heat pump, geyser and showerheads and examined for these organisms using amoebal enrichment and molecular techniques.   Amoeba could be cultivated from 45 (65.2%) of the water samples and 56 (64.4%) of the biofilm samples. The study confirmed the presence of Legionella pneumophila, Pseudomonas aeruginosa and nontuberculous mycobacteria in the hot water systems at both of the simulated winter (20°C to 30°C) and higher summer (40°C to 55°C) temperatures as well as the control system.  There was a significant positive correlation between the presence of Acanthamoeba and the presence of Pseudomonas. Based on this association it is suggested that Pseudomonas aeruginosa could be investigated as an indicator organism for the presence of Acanthamoeba and opportunistic pathogens.