– FLAGSTAFF, Arizona — A relatively new type of
drug-resistant Staphylococcus aureus could represent
the world’s next bacterial epidemic, an environmental
health expert said here today at a conference for
The superbug, called methicillin-resistant Staphylococcus aureus
strain 398, or MRSA ST398, was first identified in an infant in the Netherlands in 1994 and
traced back to her family’s pigs.
Now, researchers are starting to see more serious infections and some of the cases reveal
no direct link to livestock, said Lance B. Price, director of the Center for
Microbiomics and Human Health at The Translational Genomics Research Institute
(TGen), in Flagstaff. “The rate of human [ST398] infections is going up in Denmark
and the Netherlands,” Price said. “We are just looking at the beginning of an
epidemic.” Price made his comments during a presentation at the 49th annual
New Horizons in Science meeting, organized by the Council for the Advancement
of Science Writing. The mechanism for transmission in these newer ST398 cases
currently is unknown. Researchers are considering various explanations including
human-to-human exposure, contaminated meat or changes in the organism that make it spread
One in ten pigs gets the MRSA bacterium in livestock transport trucks, while sixty percent of pigs in slaughterhouses have the bacterium. Wageningen University veterinary researcher Els Broens finds this ‘very disconcerting’.
Broens trailed 117 pigs from the farm to the slaughterhouse. She inspected them for the presence of MRSA before and after the journey to the slaughterhouse, and after they were sedated before the slaughter. While none of the pigs had MRSA before the journey, 10 percent of them tested MRSA-positive afterwards. After the sedation in the slaughterhouse, the bacterium was found in sixty percent of the pigs. This research work was carried out jointly by Wageningen UR, the National Institute for Public Health and the Environment (RIVM) and the Animal Health Service (GD).
Already, ST398 was recently found in about half of the pigs and farmers tested in Iowa. ST398 probably started out as a human-associated strain that was treatable with methicillin, a recent analysis by Price and his colleagues has revealed. Animal husbandry practices subsequently allowed the strain to spread into livestock.
Meat production worldwide involves the use of life-saving human-class antibiotics as a preventive measure or production tool to keep animals healthy. However, the bacterial die-off then exercises a selection pressure on the remaining smaller population of bacteria, giving rise to antibiotic-resistant strains.
With ST398, that probably led to drug-resistant strains of the bug, which were then passed back to humans via contact with livestock. “It’s a pretty sad cycle really,” Price said. Staph aureus infections can cause skin and soft tissue infections, respiratory tract infections like pneumonia, bacteremia (the presence of bacteria in the blood) and endocarditis (inflammation of the inner heart).
Until the use of antibiotics in the developed world became widespread in the 1940s, these infections were often fatal. A rise in antibiotic-resistant bacteria in the past two decades means the door is open to a return to a dire medical scenario that prevailed nearly a century ago. In fact, even now, methicillin-resistant Staph aureus kills more people in the U.S. than HIV, Price said.
Industrial-scale livestock farming practices are often the culprit in the proliferation of antibiotic-resistant strains of bacteria. There are 9 billion livestock animals in the U.S. (mostly broiler chickens) and 29 million pounds of active antibiotics are administered to food animals in this country each year. The animals are raised in crowded and perhaps filthy settings.
The result is a profitable meat industry that makes this food affordable for much of the nation’s population (at a significant, long-term environmental cost when scaled up to current levels) but also one of the most effective systems for the evolution and transmission of antibiotic-resistant strains of bacteria that an engineer could devise, Price said. These strains persist on animal carcasses and then are passed on to humans via the meat we purchase and eat. –Scientific American
In the past several years, methicillin-resistant Staphylococcus aureus (MRSA) has received increased media attention. The bacterium was associated primarily with post-surgical infections or infections acquired after prolonged stays in health care facilities (such as nursing homes) or in people with weakened immune systems.
More attention was called to the pathogen when media began to report on infections acquired outside of health-care facilities. These community-acquired infections happened in locker rooms, gyms, military facilities, prisons and day-care facilities, among other places. These reports heightened concerns because the people affected were not considered to have weakened immune systems or other underlying conditions that would predispose them to infection.
Companion animals including cats, dogs and horses have been found to carry MRSA. Studies have found that veterinarians and others in close contact with these animals also may carry the bacterium.
In late 2007, attention was called to the pork industry and its products when the media reported on a study by Canadian researchers that found MRSA on pig farms2. MRSA had previously been reported in pigs and pork products in Holland in 20063. Since then, research conducted in the United States also has found MRSA in pigs in some farms and in a small proportion of pork products. MRSA also has been reported in pork producers and veterinarians who visit pig farms.
MRSA kills more Americans than AIDS
Causes, incidence, and risk factors
MRSA is a strain of Staphylococcus aureus (S. aureus)
bacteria. S. aureus is a common type of bacteria that
normally live on the skin and sometimes in the nasal
passages of healthy people. MRSA refers to S. aureus
strains that do not respond to some of the antibiotics
used to treat staph infections.
The bacteria can cause infection when they enter the
body through a cut, sore, catheter, or breathing tube.
The infection can be minor and local (for example, a
pimple), or more serious (involving the heart, lung,
blood, or bone).
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WebMed Slideshow: Closer Look at MRSA
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