WASHINGTON, August 5, 2013- The heavy use of antibiotics on industrial livestock farms may be behind the rise of antibiotic resistant superbugs, according to a recent study by scientists from Johns Hopkins, the University of North Carolina, and George Washington University. Researchers published their findings in July in the journal PLOS One.
Performed among livestock workers and their household members at hog farms in North Carolina—second only to Iowa in hog production in the country—the study is the first of its kind in the United States.
The study divided subjects into two groups: those who work on industrial hog farms where the use of antibiotics is common practice, and those who work on farms that do not use antibiotics. Using a nasal swab from the workers and their household members to detect and identify newer strains of infectious bacteria, the results of the study were startling even to its authors.
Researchers found that while staph bacteria, including Methicillin-Resistant Staphylococcus aureus (MRSA), were present in the noses of both industrial farm workers and workers on antibiotic-free farms, MRSA was found at nearly twice the rate in industrial farm workers.
One resistant strain in particular, MRSA ST 389, also known as “pig MRSA” or “livestock-associated MRSA,” was present in the nostrils of 13 of the 41 industrial farm workers who had bacteria in their nose, and in only one of the 42 antibiotic-free farm workers who had bacteria in their nose.
“We never expected to see something so clear at the outset of the study,” said Christopher Heaney, corresponding author and assistant professor of environmental health sciences and epidemiology at the Johns Hopkins Bloomberg School of Public Health last week.
Antibiotic resistance, MRSA and MRSA ST398
Responsible for 19,000 yearly deaths in the U.S. and nearly 365,000 hospitalizations, according to a study published in the Journal of the American Medical Association, MRSA is attributable to more yearly deaths and hospitalizations than AIDS.
MRSA is an antibiotic- resistant staph infection that can cause pneumonia, meningitis, toxic shock, skin abscesses, heart valve infections and other serious medical conditions that can often lead to death. Many strains of s. aureus are now resistant to antibiotics including oxacillin, penicillin, and amoxicillin. Newer strains are even developing resistance to stronger drugs like methicillin and vancomycin, used as last resort drugs in the past.
Most common MRSA infections occur in hospital settings, but community-associated (gym, sports) MRSA and livestock-associated MRSA infection is on the rise.
MRSA ST398, was first spotted in the Netherlands in 2004. It was found in the toddler daughter of pig farmers as well as in their pigs. Having spread widely in agriculture, hospitals, and supermarket meats throughout Europe, ST398 has only been documented in the U.S. in Iowa and now North Carolina.
How bacteria are becoming antibiotic resistant
Helping animals grow faster and put on more weight, industrial farms in the U.S. have been using antibiotics in livestock feed since the 1940s as a way to increase profits. Many industrial farms also use antibiotics to compensate for crowding, high stress levels among the animals, and unhygienic conditions.
Antibiotics used on domestic food-producing animals now accounts for over 80% of the antibiotics market in the U.S. Almost 30 million pounds of antibiotics were used on livestock in 2011, up 22% since 2005, according to the FDA and the Animal Health Institute.
Studies have found that when an otherwise healthy animal is fed antibiotics, over time weaker bacteria are eliminated, allowing for the dominance of strains that can withstand the drugs. Bacteria that are resistant to one type of antibiotic can often tolerate others and pass this trait on to their offspring and other microbes.
How antibiotic resistant bacteria from industrial farms infect humans
Once an antibiotic resistant bacterium is present in an industrial livestock facility, it can infect humans in a variety of ways, including through food, the environment, or direct contact with the animals.
Antibiotic resistant bacteria can reach humans who eat meat from industrial livestock operations. A recent study by National Antimicrobial Resistance Monitoring System (NARMS) found alarming rates of antibiotic resistant bacteria in retail meats.
Several medical specialists and public health officials in the U.S. and Europe have warned that consuming meat with antibiotics is contributing to antibiotic resistance in humans, as world health authorities are registering alarming levels of antibiotic resistance among the world’s population.
There are also several ways in which antibiotic resistant bacteria can enter the environment and then make the jump to humans. One major vehicle is animal manure. Industrial livestock farms produce over one billion tons of concentrated animal waste every year. Some studies estimate that roughly 75 percent of antibiotics given to animals are not digested and make up a large part of the concentrated animal waste discarded into the environment.
Much of this animal waste is sprayed on fields that surround industrial livestock operations, and can often contaminate human drinking wells if the antibiotic resistant bacteria in the manure leech into surface and groundwater. Insects that come in contact with the animal waste can also carry antibiotic resistant bacteria and infect nearby communities.
How to stop the rise of the superbug
This study is the first to show a clear link between the spread of antibiotic-resistant bacteria and exposure to animals routinely fed antibiotics. The authors admit, however, that there is more research to be done. For one thing, researchers were not allowed access to the hogs, and therefore were not able to confirm the presence of ST398 in the animals.
Despite the growing evidence that feeding antibiotics to livestock can pose serious risks to humans, the FDA has done little to regulate this practice. Unlike Europe, livestock operations in the U.S. generally refuse access to their facilities or data to the public health research community unless forced to do so by law. Unfortunately, there are very few if any laws that promote this kind of information sharing.
The FDA recommended last year that antibiotics in farm animals “should be limited to those uses that are considered necessary for assuring animal health,” calling the use of antibiotics with the sole purpose of fattening an animal “injudicious.” However, this guidance is not mandatory and farmers are free to do as they like.
In July, Senators Kirsten Gillibrand (NY), Dianne Feinstein (CA), and Susan Collins (ME) introduced the bipartisan Antimicrobial Data Collection Act, calling for “increased data collection by the FDA, enhanced transparency and public awareness of antimicrobial drug use in agriculture and strengthened FDA accountability regarding unsafe antimicrobial drug use.”
Congresswoman Louise Slaughter of New York introduced the Preservation of Antibiotics for Medical Treatment Act last March, to amend the Federal Food, Drug, and Cosmetic Act banning non-therapeutic use of eight classes of antibiotics.
This bill too has been referred to committee, and like the bipartisan bill, has little chance of going any further.
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