scientists identified a new strain of methicillin-resistant Staphylococcus aureus (MRSA), the powerful bacteria that has been responsible for more deaths in the U.S. than HIV/AIDS. The new strain’s genetic makeup is different enough from previous MRSA strains that the popular polymerase chain reaction technique (PCR) tests would fail. “That means that the molecular tests most often used to confirm MRSA status will be falsely negative if we don’t take into account the new strain,
The study began with a scientific curiosity. Dr. Laura Garcia-Alvarez, the lead author on the paper, discovered something strange while researching mastitis, a bacterial infection in cows, as a Ph.D. student at Cambridge. The S. aureus bacterium she found during her work was able to grow despite the presence of antibiotics — a pretty clear sign that it was antibiotic-resistant. Yet strangely, when Garcia-Alvarez and her colleagues used the standard molecular tests on the strain, it came back negative for MRSA. The PCR tests were unable to find the mecA gene, which is responsible for methicillin resistance.
Though the first strain was found in cows, subsequent testing found similar new MRSA strains in human beings in Scotland, England and Denmark, along with Ireland and Germany. The new strain has apparently been around for some time — the first Danish sample with it dates back to 1975 — and there’s been an upward trend in the strain over recent years. Not a huge upward trend: there are likely less than 100 isolations of the new strain each year in Britain.
The next question is where the new strain originated. cows are a likely reservoir, but they haven’t proved it yet; research is ongoing. The concern is that if cows do harbor the MRSA strains, they could transmit them to farm workers — and from them, into hospitals and the community.
MRSA is, but it’s not something you should be all that worried about. (Even if your possibly carcinogenic cell phone turns out to have MRSA all over it.) Many of us carry MRSA inside our bodies and are none the worse for the wear. Now mutant E. coli — that might be a different story.