Published: Feb. 13, 2004

Note to Editors: Contents embargoed until 11:30 a.m. EDT on Feb. 14.

Two new studies led by University of Colorado at Boulder biology Professor Norman Pace indicate trillions of microorganisms may be living on a single home vinyl shower curtain or in the air hovering over indoor pools and hot tubs.

Preliminary results indicate the formation of microbial communities known as bio-films on shower curtains are potential reservoirs of pathogens, especially dangerous to people with immune deficiencies, said Pace, a professor in the molecular, cellular and developmental biology department. Pace estimated "billions" of microbes, which he refers to as "soap scum," reside in a one-inch square of a normal used home shower curtain.

Pace and his team conducted an analysis of ribosomal RNA genes obtained by polymerase chain reaction, or PCR, from four shower curtains in Boulder, Colo. Particularly abundant sequences included the bacteria Sphingomonas and Methylobacterium, known to include opportunistic pathogens.

"Soap scum is a lush bed of microbes generally embedded in a bio-film matrix," said Pace. In general, the researchers concluded different shower curtains tended to be home to the same type of organisms.

In addition to Pace, the shower curtain study was done by former CU-Boulder graduate student Ulrike Theisen , Pace's former graduate student and Professional Research Assistant Allison St. Amand, as well as postodoctoral researcher Scott Kelly of San Diego State University and postdoctoral researcher Largus Angenent, another of Pace's graduate students now at Washington University in St. Louis.

Although the results suggest shower curtains harbor potentially opportunistic pathogens that can threaten some people, exposure to pathogens can be minimized by regular cleaning or changing to new shower curtains, said Pace.

A second study led by Pace and his colleagues undertaken at a Midwest indoor swimming pool and hot tub found that the number of microbes, many pathogenic, were enriched just above the water level by as much as 60 percent.

"These infectious microbes are especially dangerous to people with compromised immune systems," said Pace, who received a $500,000 MacArthur "Genius Grant" in 2001 and is internationally known for his studies on the range and diversity of microbial life.

In addition, a disease known as "Lifeguard Lung" caused by pathogens hovering over the water can infect pool workers, affecting their lungs and breathing patterns. The study of indoor hot tubs indicated similar pathogens just above the water surface as well as huge amounts of mycobacteria collected from hot tub filters over the course of a year.

"These findings are a bit scary," Pace said. "The bottom line is people should be aware of the risk of swimming in indoor pools or sitting in indoor hot tubs."

A similar danger exists with a pathogen called Microbial Avian Complex, or MAC, commonly found in potting soil, said Pace. It essentially works the same way as pool pathogens, with the micro-bacteria emerging from potting soil that has been mixed up by indoor gardeners as they plant flowers and plants.

Pace gave a talk on the subject at the annual American Association for the Advancement of Science conference held in Seattle Feb. 12 to Feb. 16.

Pace received the 2001 Selman Waksman Award in Microbiology from the National Academy of Sciences, the nation's highest award in microbiology. He has traveled 14,000 feet under the sea in a submarine and probed the Yellowstone Hot Springs in Wyoming for microbes living in extreme environments.

Pace is a member of the National Academy of Sciences and the American Academy of Arts and Sciences.

He has published more than 200 research articles in journals such as Science, Nature and the Proceedings of the National Academy of Sciences. He also is a fellow of the American Association for the Advancement of Science and the American Academy of Microbiology.