Amoeba Scoffs At Chlorine In Water Pipes

“Brain-Eating Amoeba” Scoffs At Chlorine In Water Pipes

The “brain-eating amoeba”  Naegleria fowleri  has grabbed headlines from New Orleans to Karachi, as its victims contract the rare but deadly pathogen after getting water up their noses. Increasingly, experts have traced the source of infection to drinking water pipes, where chlorine disinfection ought to be killing the amoeba. But a new study proves for the first time that biofilms coating drinking water pipes help N. fowleri  evade death by chlorine (Environ. Sci. Technol. 2015, DOI:10.1021/acs.est.5b02947).

N. fowleri  is a free-living single-celled organism that grazes on bacteria in lakes, rivers, and soil. People can drink water containing the amoeba and not get sick because the digestive system will kill the pathogen. But if a person inhales water,  N. fowleri  can penetrate nasal mucus and work its way to the brain where the body’s immune response sets off brain swelling, triggering primary amoebic meningoencephalitis (PAM). The disease is rare but kills more than 97% of infected people.

“Most cases of PAM arise from freshwater sources such as lakes, but an increasing number are linked to drinking water systems,” says study coauthor Geoffrey J. Puzon, a microbiologist at Australia’s Commonwealth Scientific & Industrial Research Organisation. In pure water cleared of other microorganisms, the infective form of  N. fowleri  dies after a 5-minute exposure to a chlorine concentration of 0.5 mg/L, roughly the recommended level for water systems.

But water networks aren’t so clean. Some microbes naturally inhabit the systems, forming a slippery biofilm of cells and organic matter on pipe walls. Other researchers have shown that water in such systems requires longer disinfection times and higher concentrations of disinfectant to kill common pathogens because the biofilm absorbs free chlorine, reducing its concentration in the water. “So we wondered if pipe biofilms could be protecting  N. fowleri  from disinfectants,” Puzon says.

“In the real world, biofilms get mobilized and sloughed off pipes, so we wanted to see what happens in that situation,” he says. He and his team sampled a biofilm containing naturally occurring  N. fowleri  from a drinking water pipe, suspended it in tap water, and subjected the mixture to increasing levels of chlorine. At the same 0.5 mg/L that kills the amoeba in 5 minutes without other microorganisms present,  N. fowleri  mixed with biofilm survived for 24 hours.

Source: C&EN

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