Pipe-dwelling bacteria use slimy strategy.

Pipe-dwelling bacteria use slimy strategy

Some infectious microbes can establish thriving colonies in the plastic pipes commonly used to carry water, thwarting all attempts to flush them out. Investigators have now unraveled the mechanism by which one such organism resists even the harshest germicide attacks. Their findings suggest pharmaceutical manufacturers should take aggressive steps to keep their distribution pipes whistle-clean.

The colonizers in question belong to the genus Pseudomonas and commonly live in soil and water. Although these bacteria rarely cause disease in healthy people, some can cause serious and even fatal inspections in people with compromised immune systems, open wounds or medical implants.

In the past decade, several reports have linked infectious outbreaks among hospital patients to Pseudomonas-fouled batches of an iodine solution routinely used to clean medical equipment and to disinfect skin before surgery. Those reports surprised disinfectant manufacturers, who assumed iodine would kill any stray microbes that got into it.

Scientists subsequently found Pseudomonas could survive in bottled iodine solution for up to 15 months, and government researchers fingered plastic distribution pipes used in the manufacturing process as the source of the contamination. That federal team has now developed a laboratory model that explains the microbe's extraordinary ability to shield itself against germicides.

Roger L. Anderson and his colleagues at the Atlanta-based Centers for Disease Control took plastic pipes and filled them with water contaminated with two strains of Pseudomonas. After allowing the bacteria to incubate for eight weeks, the scientists emptied out the infested water and doused the pipes with germ-killing chemicals, including chlorine and an iodine disinfectant, for seven days. They then refilled the pipes with sterile water and periodically sampled the "clean" water. In the January AMERICAN JOURNAL OF PUBLIC HEALTH, the team reports that both strains survived in the chemically treated pipes and reestablished colonies there.

The research suggests Pseudomonas has a clever way of eluding its attackers: It secretes a sticky slime that builds up on the pipe interior. A germicide flushed through a water distribution system kills free-floating microbes, but it can't touch bacteria embedded in the slimy biofilm. "You have a continuous reservoir of microorganisms that could contaminate water flowing through pipes," Anderson notes.

For manufacturers piping iodine disinfectant from one processing point to another, the findings suggest that free-floating bits of biofilm that break off during production remain impenetrable and can foul the iodine solution itself, Anderson warns.

That's just what happened to one Chicago manufacturer whose disinfectant picked up Pseudomonas while flowing through plastic pipes leading from a storage tank to the plant's bottling area. The company eliminated the problem by replacing its plastic pipes with stainless steel ones and regularly flushing them with scalding water to kill floating microbes and prevent biofilm buildup, Anderson says. Firms using plastic pipes -- which may not withstand scalding -- can instead mechanically scrape away the matrix of microbes and slime that coats interior pipe walls, says biofilm researcher J. William Costerton at the University of Calgary in Alberta.

Scientists already are seeking new types of plastic that prevent bacteria and their slime from adhering to the surface, notes Warren Litsky of the University of Massachusetts at amherst in an editorial accompanying the research report. Such an advance would reduce the threat of contamination in pipes used to manufacture disinfectant or carry water in hospitals, homes and whirlpool facilities, Anderson adds.

A victory over microbial settlers would also reduce infection risks in people who rely on plastic or metal implants such as artifical heart valves or pacemakers, Litsky says. A biofilm can shield microorganisms from antibiotic treatment, causing repeated bouts of infection for such patients, Costerton adds.