MRSA: Worse in Community Than Hospital?

Nov. 12, 2007 -- Drug-resistant staph infections caught in the community may be more dangerous than those found in hospitals, according to a new study.

Researchers found the community-associated methicillin resistant Staphylococcus aureus (CA-MRSA) bacterium secretes agents that attract and destroy immune cells that are supposed to protect against infection.

CA-MRSA infection is a global health issue because new strains of these staph bacteria have become resistant to treatment with many antibiotics and can cause severe infection in otherwise healthy individuals.

Although much attention has been paid to the hospital-associated strains of the bacterium, researchers say the findings show that the strains in the community may be more serious and difficult to treat.

New Clues on MRSA

In the study, Michael Otto, PhD, and colleagues at the National Institute of Allergy and Infectious Diseases' (NIAID) Rocky Mountain Laboratories identified peptides (building blocks of protein) called PSM that are secreted by CA-MRSA. The results appear in Nature Medicine.

These peptides appear to destroy healthy immune cells that would normally fight against the infection.

Researchers developed test strains of CA-MRSA based on widespread strains of the bacterium, identified the PSM genes within them, and performed lab tests on mice.

The results showed that the gene cluster responsible for production of PSM proteins played a critical role in the bacterium's ability to produce disease by attracting and then destroying important immune cells. Researchers say this group of genes may not be the only element affecting CA-MRSA disease severity, but it plays a major role.

They also compared PSM production from CA-MRSA with hospital-associated MRSA and found that the CA-MRSA produced more PSMs in lab tests.

"This elegant work helps reveal the complex strategy that S. aureus has developed to evade our normal immune defenses," says Anthony S. Fauci, MD, director of the NIAID. "Understanding what makes the infections caused by these new strains so severe and developing new drugs to treat them are urgent public health priorities."