Washington, January 22 : Ongoing research at the National Institute of Allergy and Infectious Diseases (NIAID), a component of the National Institutes of Health in the US, has highlighted the evolution and resilience of the bacterium methicillin-resistant Staphylococcus aureus (CA-MRSA).
In one study, it has been found that the USA300 strain of the bacterium, which is the primary cause of CA-MRSA infections, comprises of nearly identical clones that have emerged from a single bacterial strain.
With an eye on understanding how CA-MRSA is evolving in complexity and spreading geographically, the researchers sequenced the genomes of the USA300 bacterium samples obtained from 10 patients, who were among individuals treated at different US locations between 2002 and 2005.
Upon comparison, eight of the 10 samples were found to have nearly indistinguishable genomes, suggesting that they originated from a common strain. The remaining two bacteria were related to the other eight, but more distantly.
The researcher also observed that two of the eight nearly indistinguishable USA300 samples caused far fewer deaths in laboratory mice than the others, suggesting that tiny genetic changes among evolving strains could profoundly affect disease severity and the potential for drug resistance to develop.
"The USA300 group of strains appears to have extraordinary transmissibility and fitness," says Frank R. DeLeo of NIAID's Rocky Mountain Laboratories (RML) in Hamilton, who led the study appearing online in the Proceedings of the National Academy of Sciences.
"We anticipate that new USA300 derivatives will emerge within the next several years and that these strains will have a wide range of disease-causing potential," he adds.
Another study led by the same research team, and recently published online in the Journal of Immunology, provides new details about the complex mechanisms that MRSA uses to avoid destruction by neutrophils, human white blood cells that ingest and destroy microbes.
The researchers observed that MRSA senses danger when it is exposed to the killer chemicals released by neutrophils-such as hydrogen peroxide, hypochlorous acid (the active component of household bleach) or antimicrobial proteins.
The bacterium then escapes harm and turns the tables on the white blood cells, destroying them.
DeLeo's team is continuing its research to determine how the bacterium senses and survives attacks by neutrophils.