Sole survivors: Bacteria build up on shoe bottoms


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Dr. Chuck Gerba, an environmental microbiologist at the University of Arizona, says he doesn't put his shoes up on his desk anymore -- not since completing a study dealing with the accumulation and elimination of E. coli and other nasty fecal-based bacteria on soles.

The study, funded by Rockport in conjunction with introduction of its latest line of washable leather shoes, showed that just one wash cycle could eliminate almost 99 percent of the bacteria, Dr. Gerba said. Some 30 test subjects wore washable shoes for the study, while another group wore more conventional shoes that couldn't be washed.

Besides E. coli, which is known to cause intestinal and urinary tract infections, the soles of the shoes picked up Klebsiella pneumonia bacteria, a source of wound and bloodstream infections as well as pneumonia, and Serratia ficaria, a rare cause of infections in the respiratory tract and wounds.

Those bacteria, Dr. Gerba said, all are found in fecal material, and apparently were picked up from floors in public restrooms and outside from animal excrement. The study also showed the bacteria lived longer than usual "because you're accumulating food [for the bacteria] on the bottom of the shoes," he added.

"[The shoes] look like they're becoming a bacteria cafeteria. ... We didn't do a survival time, but they were surviving longer than they would on a desk top."

Dr. Gerba, who studies how diseases are transmitted through the environment, said that once-a-month laundering probably was sufficient to hold down external bacterial contagion.

Also cleaned at 90 percent efficiency in the laundry were a different type of bacteria, those that grow on skin and are transferred to insoles by wearing shoes without socks. "You can get other bacteria from the air and dirt [that] can go in there, too," Dr. Gerba said.

"They grow in a moist, warm environment. ... They like to live in saunas and that's basically what your shoe becomes."

Two years ago, Dr. Gerba did a similar study on purses and found that one-third of those tested at random were infected with fecal bacteria. The reason: "probably because [women] put them down on bathroom floors. They are full of bacteria."

Rockport said the scientists washed the shoes in a standard washing machine, using company-suggested conditions: cold water and 12-minute wash cycle with detergent. The shoes should be air-dried for 24 hours.


Pohla Smith can be reached at psmith@post-gazette.com or 412-263-1228.


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