The medical news this week has been dominated by the possible carcinogenicity of cell phones and the virulent E. coli outbreak in Europe. But I hope your closet of fear isn’t full yet — I’ve got one more bit of medical worry to stuff in it. In a study published Thursday in the Lancet Infectious Diseases journal, a group of British and Danish 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,” Dr. Mark Holmes, a senior lecturer in preventative veterinary medicine and author of the Lancet paper, told reporters at a press conference. “Some MRSA that may be out there may not have been detected.” 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. “We were obviously curious about what was causing the methicillin resistance, if it wasn’t the mecA gene,” said Holmes. After the Wellcome Trust Sanger Institute sequences the entire genome of the strain, the team found that it did have a gene for methicillin resistance, but one that had only 60% similarity to the original mecA gene. That’s not close enough to show up in standard molecular tests — as Holmes put it, … Continue reading Watch Out for the Cows. They Might Be Carrying a New Strain of MRSA