MICROBIOLOGY

Filed Under News 

Genes Key to Staph Disease Found Together

One of the ways Staphylococcus bacteria become drug-resistant is through horizontal gene transfer, whereby resistance genes move from one bacterium to another. Staph bacteria also can exchange virulence genes using the same mechanism, but this was previously assumed to occur separately from the transfer of antibiotic resistance. According to an article published online in PLoS Pathogens (2009;5:e1000533), a study of Staphylococcus bacteria, including methicillin-resistant S. aureus (MRSA), has discovered a potent staph toxin responsible for disease severity. The study also found the gene for the toxin traveling with a genetic component of Staphylococcus that controls resistance to antibiotics. The study, now, shows for the first time that genetic factors that affect Staphylococcus virulence and drug resistance can be transferred from one strain to another in one exchange event. The research involved more than 100 strains of S. aureus and S. epidermidis, both bacteria found on the skin of most people. In recent decades, these bacteria have become increasingly virulent, often causing severe disease that can be resistant to traditional antibiotics such as methicillin. The study found that staphylococci secrete toxins of the phenol-soluble modulin (PSM) family that are primarily responsible for attracting and killing human white blood cells called neutrophils. This process is critical for the ability of S. aureus-including community-acquired MRSA-to cause disease. While screening S. aureus and S. epidermidis strains, the research team noticed that some strains produced one additional, previously unknown PSM toxin. The researchers hypothesized that the toxin was somehow connected to drug resistance. This idea surfaced because the toxin appeared in 10% of all MRSA strains and 68% of all methicillin-resistant S. epidermidis strains analyzed-whereas the researchers did not find it in strains of S. aureus or S. epidermidis that are sensitive to methicillin. The study confirmed its hypothesis by identifying the specific location that encodes the toxin, which was in gene clusters that control drug resistance, known as SCCmec. The group named the new toxin PSM-mec. According to the authors, this work represents a previously unknown example of a toxin hitchhiking on staphylococcal mobile genetic elements that are primarily in charge of transferring antibiotic resistance, and that the findings should alert the research community that aggressive, drug-resistant staph can evolve more quickly than previously assumed. The research group is continuing its study of PSM-mec in S. epidermidis, where the toxin is more prevalent. Ultimately, being able to neutralize PSM-mec and other toxins that attack human defenses could lead to new treatments for S. aureus and S. epidermidis disease.

Comments

Leave a Reply

You must be logged in to post a comment.