MRSA found in cow’s milk

By Dr. Ananya Mandal, MDJun 5 2011

Scientists have discovered a new strain of the drug-resistant germ known as MRSA in cow’s milk and some evidence that the animals could be a source of the infection in humans.

The team from University of Cambridge was studying an infection of the animals’ udders, according to an article published in the U.K journal The Lancet Infectious Diseases when they stumbled upon this finding. Tests showed that people in Scotland, England and Denmark carried the new variant of MRSA, or methicillin-resistant Staphylococcus aureus, and that the bacteria can elude the usual means of detection.

They found that tests that search for the mecA gene, which enables the bacteria to resist treatment with some antibiotics, can miss the new, genetically different strain, researchers said. Relying solely on gene testing can lead doctors to prescribe medicines that are powerless against MRSA, the researchers added. Mark Holmes, the lead researcher said, “It’s important that any of the MRSA testing that is based on detection of the mecA gene be upgraded to ensure that the tests detect the new gene found in the new MRSA.”

Till date the usual molecular screening for MRSA searches for the mecA gene. The new strain has a mecA gene that’s only 60 percent similar to the original version, leading to a false negative result when tested, the study found.

The authors write that in spite of the fact that the new strain can cause disease in people, the risk of becoming infected is low. Further study is planned to determine how prevalent the new strain is and where it’s coming from, the researchers said.

“Even though this new strain isn’t picked up by the current molecular tests, they do still remain effective for the detection of over 99 percent of MRSAs,” said Angela Kearns, head of the U.K. Health Protection Agency’s Staphylococcus Reference Laboratory, in a statement.

Further the team also found evidence that cattle could be a key reservoir of the new strain of MRSA. The samples found in humans were either of a strain thought to be unique to animals or other types detected in cattle, the study said. In England, the researchers found a geographical association between human and animal isolates of MRSA. Pasteurization of milk will prevent infection, they assured.

MRSA can occur in hospitals or in otherwise healthy people who come into contact with the bacteria in settings such as locker rooms or day care centers, the NIH said. Infections cause a red, painful, swollen area on the skin, and symptoms of severe cases include chest pain, chills, fatigue, fever and shortness of breath.