Scientists Find MRSA Germ in Supermarket Meats

WEDNESDAY May 11, 2011 -- MRSA, a bacteria resistant to common antibiotics, has been discovered in supermarket meats, and the germ is apparently being introduced by human food handlers, a new study reports.

Although thorough cooking will kill the bacteria, consumers run the risk of infection if they handle meats contaminated with the germ, researchers said.

MRSA (methicillin-resistant Staphylococcus aureus) is common in hospitals and nursing homes, where it can cause serious illness and even death. And so-called "community-acquired MRSA" has become a problem among some high school and college athletes who share equipment; this type of MRSA appears as a skin infection and is usually less serious, according to the U.S. Centers for Disease Control and Prevention.

It's the community-acquired MRSA that was found in the meats, the researchers said.

"MRSA has always been found in human patients, but we found this in retail meat, so retail meat can be a reservoir of these bugs," said study lead researcher Yifan Zhang, an assistant professor in the department of nutrition and food science at Wayne State University in Detroit.

"When people handle food, they can get the bugs from the meat if the meat is already contaminated," she explained.

The risk of becoming infected is especially high if you have open cuts or sores on your hands or skin, Zhang added.

"When you handle food, especially if you have wounds on your hands, wear gloves to protect yourself from getting MRSA infection," she said.

The researchers found a human strain of MRSA in meats, so people can also transfer the bacteria to meat, she added.

Contamination can occur if carriers of MRSA handle meat or if there is MRSA in the environment, which might happen in processing plants where the meat is processed, Zhang added.

The report was published in the May 11 online edition of the U.S. Centers for Disease Control and Prevention's journal Emerging Infectious Diseases.

For the study, Zhang's team purchased 289 raw meat samples, including 156 beef, 76 chicken and 57 turkey samples, from 30 grocery stores in Detroit from August 2009 through January 2010.

The researchers found that 22.5 percent of the samples were contaminated with S. aureus and six samples tested positive for MRSA. Of the six samples contaminated with MRSA, two were beef, three were chicken and one was turkey, the researchers said.

The extent of MRSA contamination in meat varies by the type of meat and where the meat was processed, Zhang said.

Zhang thinks that MRSA in meat results from contact by people carrying the bacteria. Another recent study found that the strain of MRSA in meat in the United States is not the strain found in animals, she noted. That strain is found more commonly in Europe, she added.

However, the animal strain of MRSA has been found in live pigs in the United States, so it may appear in the food chain in the future, the researchers added.

Dr. Marc Siegel, an associate professor of medicine at New York University, said that "MRSA is a big problem and appears to be invading our meat."

Siegel also believes that the MRSA contamination Zhang's group found is most likely from infected people handling the meat.

Another factor is the overuse of antibiotics in the raising of livestock. This, Siegel explained, could create antibiotic-resistant animals that are more likely to be susceptible to bacteria such as MRSA.

"The combination of the overuse of antibiotics and the fact that MRSA is becoming more prominent in the human population explains this," he said.

In addition to taking other precautions when handling meat, MRSA is killed when the meat is cooked thoroughly, Siegel added.

Siegel also suggested washing plates or utensils used to prepare food before using them again to eat. And, it is important to disinfect counters that have come into contact with meats, he advised.

These precautions would also kill off any other S. aureus, which "we don't need in our meat either," Siegel said.

On a positive note, another report in the same journal issue finds that efforts to reduced bacterial contamination of chicken from campylobacteriosis have resulted in a 50 percent drop in what was an epidemic in New Zealand.

More information

For more information on MRSA, visit the U.S. National Library of Medicine.

Posted: May 2011


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