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Bacteria Gone Bad

– Lauren Stanchek


The disease that sent you to the hospital may not be the one that keeps you there. Two million people each year acquire a secondary infection in the hospital, according to the national Centers for Disease Control and Prevention. And ironically, the patients who can least defend against it — intensive care patients — are at the highest risk.

Breaking the skin to insert a device such as a catheter, shunt or implant allows bacteria that normally live on the surface to enter the body. Many bacteria, such as a normal inhabitant of human skin called Staphylococcus epidermidis, secrete slime that protects them and helps them stick to the plastic surfaces of the device.

“It’s kind of insidious because it forms this slime layer,” said UGA doctoral student Jonathan Moon, who studies under biochemist James Travis. “You can treat it with an antibiotic and it’ll seem like the infection is gone. But because it has that protective layer, sometimes the antibiotic can’t infiltrate all the way through and infection will recur later.”

Moon studies this normally non-pathogenic organism to learn how it can cause disease. His work focuses on the function of proteinases, or proteins that chew up other proteins, because scientists believe proteinases play a role in disease progression.

To attack other proteins, proteinases seek out a particular entry point: They look for sequences of amino acids on a target protein and then dig in at that point.

Moon found that S. epidermidis contains a proteinase similar in structure and function to a virulent protein in S. aureus, a pathogenic bacterium that causes sties, boils and toxic shock syndrome. He has identified the first amino acid in the proteinase’s target sequence. Now Moon said he plans to determine the rest of the sequence with help from a collaborator in California.

“So given that information, sometimes you can take that sequence and map it back to possible targets,” Moon said. In this way, researchers can predict which human proteins might be attacked by the proteinases of pathogenic organisms.

According to Moon, the S. epidermidis proteinase appears to degrade several proteins, including the protein in blood that functions in clotting. In experiments, the proteinase “would either extend the time it took blood to clot or completely eliminate clotting,” Moon said.

While his work on S. epidermidis continues, Moon also is studying proteinases produced by Penicillium marneffei, an opportunistic fungus native to Southeast Asia. The fungus can spread in people who have weakened immune systems, such as people with AIDS. But people with healthy immune systems easily overcome such fungi.

Previously scientists believed that P. marneffei produced no detectable proteinases. Moon and his coworkers thought otherwise.

“We took issue with that because you could grow the fungus in the lab on a medium that consisted of only a whole protein as the nitrogen source, which suggested that it’s got to break down that protein somehow — and you only do that with a proteinase,” Moon said.

Moon’s research on proteinases eventually could lead to an understanding of their role in the progression of disease, especially in patients whose immune systems are compromised.

For more information, contact



Research Communications, Office of the VP for Research, UGA
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