Mrsa | Combating MRSA: Researchers Study Toxin


Dec. 4, 2012 — The Caenorhabditis elegans , a small worm called a nematode, scurrying across a Petri dish has helped lead to discoveries about community-associated MRSA (methicillin-resistant Staphylococcus aureus ).

“In the last year this organism has killed more people in the United States than AIDS,” said Kathleen Dannelly, an Indiana State University associate professor of biology leading the community-associated MRSA study. “It’s going to get worse.”

MRSA identifies a staph infection that is unable to be defeated by most penicillin-based drugs. Community-associated MRSA varies from the hospital-related one, which tends to be a more virulent strain picked up by people admitted to hospitals. Community-associated MRSA can cause toxic shock syndrome or blood and bone infections.

“They’ve picked up this incredible invasiveness mechanism that we don’t understand at all,” Dannelly said. “It’s frightening what it can do.”


A normal staph infection looks like a boil and remains in the skin. With MRSA, in the worst strains, the bacteria can eat down through the flesh to the bone in 36 hours.

Dannelly became interested in studying the community-associated MRSA in 2004 when an outbreak infected members of Indiana State University’s football team. Players who received cuts and abrasions during games and practice found themselves diagnosed with MRSA and, in some cases, undergoing surgery for it.

Many people unknowingly carry MRSA on their skin as part of their bacteria and remain uninfected as long as they receive no cuts or scrapes to allow the bacteria to enter the body, Dannelly said. Six years ago, Dannelly and her students conducted a blind sidewalk study, swabbing the noses (MRSA thrives in warm, moist places) of 500 students, faculty and staff. They found that 1 ½ percent carried MRSA bacteria. Five years later, Dannelly and her researchers again conducted the blind study and they found the number of MRSA carriers had grown to 2 percent of the study group.

“The people had no idea they were carrying it,” she said.

In the meantime, the scurrying nematode, which is only a few millimeters long, helped lead researchers to an interesting discovery. By comparing the genomes of community-associated MRSA and the staph infection, they found significant differences to investigate.

“This organism is so invasive we thought there have to be toxins that we don’t know about,” Dannelly said.

After cloning 15 genes, researchers have, thus far, purified six to determine what the proteins do. Researchers have found that MRSA’s different proteins


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