A mighty superbug may become even more powerful when a patient is treated with antibiotics.

Researchers say mice infected with methicillin-resistant Staphylococcus aureus (MRSA) actually became sicker when they were treated with beta-lactam antibiotics.

The findings by the scientists at Cedars-Sinai Medical Center in Los Angeles were published today in the journal Cell Host & Microbe.

The researchers said the beta-lactam antibiotics normally kill staph bacteria by inactivating the enzymes they use to strengthen and build cell walls.

However, one of these enzymes called PBP2A is not turned off in MRSA when the infection is exposed to the antibiotics.

In fact, the deadly superbug continues to build cell walls, and those walls are different than ones built in normal staph infections.

The Cedars-Sinai researchers said the altered cell walls have a “powerful inflammatory response.” That, in turn, made the mice treated with antibiotics even sicker.

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Implications for Human Patients

The scientists said their findings raise the possibility that prescribing beta-lactam antibiotics for humans with staph infections might be a bad idea.

An additional problem is that physicians don’t always know what strain of staph a person is infected with. It may take a day or two to determine if MRSA is indeed the culprit. That could leave doctors in a quandary over whether to prescribe these particular antibiotics.

Beta-lactam antibiotics are the most commonly used group of antibiotics. They are a first line of defense when the origin of an infection isn’t known, researchers said.

The researchers did caution that their study only dealt with mice. They said more research with humans is needed before they could make any recommendations.

“Based on this research, clinical studies are warranted,” said study author Sabrina Mueller, Ph.D. “However, pending the outcome of those studies, physicians should follow current national guidelines set by the Infectious Diseases Society of America for antimicrobial treatment of staph infections.”

Those guidelines list recommended treatments for each category of bacterial infection.

Read More: How Little Bugs Cause Big Problems in Hospitals »

MRSA a Major Problem

MRSA causes 80,000 invasive infections and 11,000 related deaths per year in the United States, according to 2011 figures from the Centers for Disease Control and Prevention.

The infection garnered additional attention last month when it was revealed that New York Giants football player Daniel Fells was treated for the ailment.

The infection is believed to have killed comedian Bernie Mac in 2008.

MRSA can infect someone by entering the body through a cut, sore, catheter, or other means. Athletes such as football players and wrestlers who come in close contact with each other are especially vulnerable to the disease.

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