National Institutes of Health (NIH) scientists and their colleagues in China, together with a collaborator at the University of California, San Francisco, have described a rapidly emerging Staphylococcus aureus gene, called sasX, which plays a pivotal role in establishing methicillin-resistant S. aureus (MRSA) epidemics in most of Asia. Senior author Michael Otto, Ph.D., of NIH's National Institute of Allergy and Infectious Diseases, says these findings illustrate at the molecular level how MRSA epidemics may emerge and spread. Moreover, the study identifies a potential target for novel therapeutics. MRSA is a leading cause of severe infections that occur predominantly in hospitals. The results were published online in Nature Medicine on April 22, 2012. MRSA epidemics happen in waves, with old clones of MRSA bacteria disappearing and new clones emerging, a process whose molecular underpinnings are not fully understood. Previous data indicated that the sasX gene is extremely rare. Therefore, the researchers were surprised when they analyzed 807 patient samples of invasive S. aureus taken over the past decade from three Chinese hospitals. Their data showed that sasX is more prevalent in MRSA strains from China than previously thought, and the gene's frequency is increasing significantly: From 2003 to 2011, the percentage of MRSA samples containing sasX almost doubled, from 21 to 39 percent. This finding suggests that the sasX gene is involved in molecular processes that help MRSA spread and cause disease. The researchers determined in laboratory and mouse studies that sasX helps bacteria to colonize in the nose, cause skin abscesses and lung disease, and evade human immune defenses.
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