Navigation Links
Key to MRSA Virulence in Community Discovered
Date:11/12/2007

Bacteria target immune system cells sent to kill them, study finds

MONDAY, Nov. 12 (HealthDay News) -- Researchers have uncovered a cache of molecular weapons that helps make community-associated methicillin-resistant Staphylococcus aureus (MRSA) so virulent.

Though more work must be done, the study "provides a partial explanation of why these strains are so successful in causing infection and gives a starting point in the development of new drug treatments," said Dr. Gregory Moran, a professor of medicine in the departments of emergency medicine and infectious disease at the Olive View-UCLA Medical Center.

Michael Otto, a senior investigator at the National Institute of Allergy and Infectious Disease, Rocky Mountain Laboratories, and his colleagues searched for and found a battery of short, novel peptides that are expressed by community-associated MRSA strains at higher levels than their hospital-associated MRSA cousins.

Deleting the genes encoding these peptides in mouse models of bacterial infection reduced the microbes' ability to kill or induce skin lesions in infected animals, while purified peptides paralyzed -- and paradoxically, activated -- neutrophils, which are the white blood cells whose job it is to prevent bacterial infections and the principal component of pus.

The study was published in the Nov. 11 online issue of Nature Medicine.

According to the U.S. Centers for Disease Control and Prevention, S. aureus, commonly found on the skin and in the nose of healthy individuals, is associated with bacterial skin infections. MRSA, as its name implies, is a particularly nasty strain of S. aureus that is resistant to the class of antibiotics that includes penicillin, amoxicillin and methicillin.

Traditionally, MRSA, which can cause boils, skin necrosis and even death, has been limited to hospital settings and crowded environments such as prisons. Yet, beginning in 1999, community-associated cases of the disease have been on the rise. Last month, a study in the Journal of the American Medical Association found that more people died of MRSA than of AIDS in 2005.

"That [sudden increase] was alarming, and nobody knew why it was happening," said Moran, who co-authored a 2006 study showing that community-associated MRSA accounts for almost 60 percent of skin infections that require a visit to the emergency room. "Something about these strains made them very well-suited to spread throughout the population."

These peptides could explain that virulence, at least in part, said Philip Tierno, director of clinical microbiology & immunology at New York University Medical Center and author of The Secret Life of Germs: Observations and Lessons From a Microbe Hunter."

"Virulence, it seems, is caused by these peptides, which can kill phagocytic cells [neutrophils], which come to your defense when staph is invading your body," he explained.

Staphylococci, Tierno noted, induce pus formation by recruiting and activating white blood cells. "That very induction of phagocytes [neutrophils] is key to your successful eradication of the organisms in the body," he said. However, "Staph has a defense. These peptides that can kill these phagocytic cells, thereby rendering you defenseless."

The genes encoding these toxins are found in the genomes of all sequenced MRSA strains, but community-associated MRSA strains produced the toxins at higher levels than the hospital strains, which typically cannot infect healthy individuals. Thus, they may explain the enhanced virulence of the community-associated strains.

The bacteria would fly under the immune system's radar, so to speak, by not expressing the peptides until the bacteria were either present in very large numbers, or perhaps after being engulfed by neutrophils and enclosed in a small space.

In either case, the mechanism would detect that situation and begin production of the peptides in earnest to fight back against the immune system.

"From the bacterial point of view, the most important thing is to get rid of the neutrophil," Otto said.

According to Moran, these findings suggest new drug possibilities -- antibodies that can remove the peptides from circulation, for instance.

"Any time we can better understand the basic physiology of how infections get around the immune system, it gives a potential target for treatment," he said.

However, Tierno emphasized that focusing exclusively on these peptides would be a mistake, as they represent just one of many mechanisms by which virulent MRSA can harm their hosts; these strains also express toxins that can overwhelm the body in other ways.

"All of these work together to make the organism so deadly," Tierno said. "There is a synergy without question that accounts for a big problem with these organisms."

More information

For more on community-associated MRSA, visit the U.S. Centers for Disease Control and Prevention.



SOURCES: Michael Otto, Ph.D., senior investigator, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Mont.; Gregory Moran, M.D., professor, Medicine, Department of Emergency Medicine & Infectious Diseases, Olive View-UCLA Medical Center; Philip Tierno, Ph.D., director, clinical microbiology & immunology, and associate professor, microbiology & pathology, New York University Medical Center, and author, The Secret Life of Germs: Observations and Lessons From a Microbe Hunter; Nov. 11, 2007, Nature Medicine online


'/>"/>
Copyright©2007 ScoutNews,LLC.
All rights reserved  

Related medicine news :

1. MedHelp to Add Top Stanford Surgeons and Specialized Forums to Online Health Community
2. Syndicom to Launch Online Community for DePuy Spine
3. Governor Rendell Proclaims Sept. 9-15 as Senior Community Center Week
4. South Texas Doctors Report More Severe Cases of Community Staph Super Bug Hospitalizing Children
5. American Diabetes Association and Goya Foods Inc. Team Up To Support Diabetes Awareness and Outreach in the Latino Community
6. Optim To Assist Prairie Community Health Center with Construction Scope Development
7. Uninsured community health center patients often have difficulty accessing specialty services
8. ASTRO, Wellness Community South Bay Cities Join to Promote Cancer Survivorship
9. Nucletron Announces Management Buy-Out to More Effectively Meet the Demands of Its Customers and the Radiation Therapy Community
10. ProAssurance Group Offers Coverage for Community Based Hospitals in Michigan
11. Free Diabetes Community Health Worker Training
Post Your Comments:
*Name:
*Comment:
*Email:
Related Image:
Key to MRSA Virulence in Community Discovered 
(Date:5/28/2016)... ... , ... After a year and a half of planning the Multiple Pathways of Recovery ... Pathways of Recovery Conference was held May 2 -4, 2016 at the Mystic Marriott ... together to explore the many pathways individuals use to get into and sustain their recovery. ...
(Date:5/27/2016)... ... 2016 , ... Two director-level employees of Horizon Blue Cross Blue Shield of ... 2016 honorees. The award recognizes businesswomen who excel in their fields and who ... the MLTSS (Managed Long-Term Services and Supports) Program at Horizon NJ Health and Theresa ...
(Date:5/27/2016)... NY (PRWEB) , ... May 27, 2016 , ... This ... of a stroke, which we as a society can control and change. , As ... occurs nearly every 40 seconds within the United States. Plus, with an estimated 129,000 ...
(Date:5/27/2016)... ... May 27, 2016 , ... Aimed ... by inspiring human interest stories, courtesy of leaders in the nursing and health ... the industry, from leading advocates and associations—namely Jones & Bartlett Learning. , Jones ...
(Date:5/26/2016)... ... May 26, 2016 , ... Despite last week’s media reports hinting at ... company to wait until March 2017 for an interest rate increase, according to Rajeev ... of Business. , “The Federal Open Market Committee (FOMC) dot charts are of interest ...
Breaking Medicine News(10 mins):
(Date:5/25/2016)... CAMBRIDGE, England , May 25, 2016 /PRNewswire/ ... genomics company employing the precision of circulating tumour ... oncology, today announces the appointment of Professor ... will provide medical leadership across the clinical development ... that Inivata,s products help deliver significant improvements in ...
(Date:5/24/2016)... 24, 2016 Cirujanos holandeses han ... a los médicos a compartir sus mejores prácticas por ... mundial. Profesionales médicos de Europa, África, Asia ... a la aplicación, que combina la transmisión en vivo ... seguro. Educación   "Imagine un médico ...
(Date:5/24/2016)... May 24, 2016  Diana Russell suffers from a ... from the inside out.  This disease has put her ... her children and grandchildren to leave her home.  Because ... family cannot haul the wheelchair.  So if there is ... and Diana is left to wait for the bus. ...
Breaking Medicine Technology: