Potentially harmful bacteria slip through antimicrobial showerheads
To protect against harmful waterborne pathogens, many consumers, including healthcare facility managers, are installing antimicrobial silver-containing showerheads. But in ACS ES&T Waterresearchers now report that these devices are not a “magic bullet.” Under real-world shower conditions, most microorganisms are not exposed to silver long enough to be killed. However, the composition of rare microorganisms in the water from these shower heads varied with each type of fixture tested.
Water droplets and mist formed during showering may be inhaled or swallowed. Installing showerheads containing silver, a naturally antimicrobial metal, is a cost-effective way to potentially prevent drinking water-associated pathogens (DWPI). DWPI, e.g. strains Pseudomonas and Legionellawhich may cause infection in people with compromised immune systems. However, researchers have previously reported that reducing DWPI by adding copper and silver to a building’s water supply to eliminate bacteria and viruses (i.e., copper-silver ionization) is a temporary or minor solution. The findings from the copper-silver ionization study have raised concerns in the scientific community that short-term exposure to silver in shower heads may enhance microorganisms and increase the risk of antimicrobial resistance rather than suppress it. So Sarah-Jane Haig and colleagues wanted to understand how silver-containing showerheads affect the microbial composition of the water.
The team compared two traditional showerheads made of plastic or metal with three fixtures containing silver – as a silver mesh within the showerhead, as a silver-coated copper mesh in the showerhead and hose, or as an embedded Silver polymer composite. Shower heads operate in Haig’s full-scale shower laboratory facility, which was developed to mimic real-world conditions.
Contrary to the manufacturer’s antimicrobial claims, silver did not reduce overall DWPI concentrations or total bacterial counts in the researchers’ shower laboratory water samples. Haigh and her team theorized that this was due to differences between their testing conditions and those of the manufacturer. More specifically, in this study, water flowed quickly from a shower head, just like what would happen when someone takes a shower. However, the standard test used by the manufacturer exposes microbial cultures to the silver material alone for 16 to 24 hours, which the team says is not an appropriate time frame or realistic scenario.
Although the overall pathogen concentrations in the water samples did not change between the standard and silver showerheads, the composition of the microbiome did. The number of populations varied for each silver-containing fixture, suggesting that the way the silver is incorporated into the shower head is important and that rare microorganisms are responsible for much of the variation. Further experiments by the team showed that microorganisms in silver-containing showerheads may be more likely to form communities of microorganisms called biofilms in response to stressful environments. Additionally, the researchers say biofilms may explain the correlation between the abundance of different species and the age of sprinklers, because these communities are reservoirs of DWPI.
“These findings highlight the need for improved testing standards, real-world performance assessment and innovative solutions to mitigate microbial risks in water systems to benefit consumers and vulnerable groups,” Haigh said.
The authors acknowledge funding from the National Science Foundation.
2024-12-18 18:17:19