Many researchers believed that the toxin Panton-Valentine leukocidin (PVL) was the cause of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) as it could be found in all CA-MRSA strains.
But new evidence strongly suggests that is not the case. A study led by National Institute of Allergy and Infectious Diseases (NIAID), shows that the two major epidemic CA-MRSA strains and the same strains with PVL removed are equally effective at destroying human white blood cells – the primary defense against bacterial infections. The findings are surprising because many scientists had presumed that CA-MRSA uses PVL to target and kill specific white blood cells known as neutrophils.
Researchers also used mouse models to learn that CA-MRSA strains are just as pathogenic with or without PVL present. These findings were seen in tests with mice that displayed skin and soft-tissue infection and bacterial sepsis.
“The strains were just as deadly with or without the PVL toxin,” says lead investigator Frank DeLeo, of Rocky Mountain Laboratories. “Unexpectedly, the average abscess volume in mice infected with strains absent the PVL was slightly greater than those containing the toxin. The strong association between PVL and CA-MRSA makes the toxin an excellent marker to track community strains, but the assumption that it is the major virulence determinant driving this epidemic is simply not true.”
One of the biggest problems with CA-MRSA skin infections is that they spread rapidly and have the potential to cause illness much more severe than traditional hospital-associated MRSA infections, where PVL is less common.
The NIAID researchers said they will shift away from PVL and try to determine exactly which toxin or other mechanism in MRSA which kills white blood cells and allows the spread of CA-MRSA infection.