From farm to table: insects as a conduit for antibiotic resistant bacteria

Standard

The love affair between industrial agriculture and the antibiotic industry has come into an uncomfortable spotlight of late. In 2011, 7.7 million pounds of antibiotics were sold to treat sick people in the United States. This compares with a whopping 29.9 million pounds of antibiotics fed to cattle, pigs and poultry.1 Regular antibiotics doses keep perpetually overcrowded animals from falling ill and dying en masse, but antibiotics are also widely used to hasten growth, shortening an animal’s time to slaughter and increasing profit.

Concentrated animal feeding operations, or CAFOs, have come to dominate the meat industry over the past fifty years. Swine operations such as the one depicted here represent an enormous source of environmental pollution and are a breeding ground for antibiotic resistant bacteria. Credit: Wikimedia commons

Concentrated animal feeding operations, or CAFOs, have come to dominate the meat industry over the past fifty years. Swine operations such as the one depicted here represent an enormous source of environmental pollution and are a breeding ground for antibiotic resistant bacteria. Credit: Wikimedia commons

What’s the consequence of all this unfettered antibiotic use? Multi-drug resistant strains, or “superbugs” are on the rise. Our ability to keep pace with resistance by producing new antibiotics is diminishing. It’s even been suggested that we’re now entering a post-antibiotic era.

In 2010, representatives of the FDA, U.S. Department of Agriculture and Center for Disease Control and Prevention testified before Congress that a definitive link exists between the overuse of antibiotics in animal agriculture and antibiotic resistant diseases in humans.

Credit: pewhealth.org

Credit: pewhealth.org

But in spite of mounting evidence, the meat industry has largely succeeded in lobbying against any antibiotic restrictions. A major thrust of the industry’s argument is the lack of direct evidence linking antibiotic resistant bacteria bred on animal farms to human disease.

Now, proponents of antibiotic regulation may have some powerful new evidence to fuel their case. Microbial ecologist Ludek Zuerkand colleagues at Kansas State University are finding that insects- particularly houseflies and cockroaches- may represent the missing link between animal farms and human population centers.

Their review paper on insects and antibiotic resistance is currently in press in the journal Applied and Environmental Microbiology.

Zurek’s research team focuses on Enterococci, a group of bacteria responsible for illnesses ranging from urinary-tract infections to meningitis. Enterococci are also rather infamous for developing multi-drug antibiotic resistance. In one study, researchers measured the abundance of Enterococci in two swine production facilities in Kansas and North Carolina. The scientists examined houseflies, roaches and pig feces collected at both sites, finding Enterococci in 89% of all samples. Multi-drug resistant strains were found everywhere. Moreover, the drug-resistant strains found in flies and roaches were genetically identical to the strains found in swine feces, indicating insects acquired their pathogens from pigs.

In another study, the researchers screened houseflies collected from five fast food restaurants in a town in northeastern Kansas. Ninety seven percent of flies harbored Enterococci. The most abundant strain, Enterococcus faecalis, showed resistance to broad-spectrum antibiotics including tetracycline, erythromycin, ciprofloxacin and kanamycin. The scientists also identified transposons- snippets of DNA bacteria can swap during conjugation, their version of sex- that are associated with antibiotic resistant traits.

Ready-to-eat food from the same restaurants was also contaminated with antibiotic-resistant bacteria. Contamination was higher in summer than winter, corresponding with increased numbers of houseflies in restaurants.

From these investigations, the researchers concluded that “food served in restaurants is commonly contaminated with antibiotic-resistant Enterococci and that houseflies may play a role in this contamination.”

The common housefly may be more than just a nuisance: new research highlights this insect's important role in spreading antibiotic resistant bacteria.

The common housefly may be more than just a nuisance: new research highlights this insect’s important role in spreading antibiotic resistant bacteria. Credit: Wikimedia commons

Not wishing to lose points for a lack of thoroughness, the scientists decided to test directly whether insects from animal farms can contaminate food. In another study, they collected flies from a cattle feedlot and brought them back to the lab. Within thirty minutes, the flies deposited roughly 1,000 antibiotic-resistant Enterococci on a hapless beef patty. This experiment was carried out using as few as five flies.

Houseflies give bacteria more than just a free ride from farm to food. They may also serve as an incubator. Several studies have shown that pathogenic strains of E.coli proliferate in the gut of common houseflies and can be transferred during feeding.

Using a fluorescent protein to tag and track bacteria, Zurek’s research team found Enteroccoccus density peaks in the fly’s crop, or foregut, roughly 48 hours after ingestion. Significantly, houseflies regurgitate the contents of their crop while feeding. In doing so, they can disseminate bacteria into their food and water.  Zurek suggests houseflies serve as a “bioenhanced vector for bacteria” because of their dual role as incubator and locomotion.

The work of Zurek and his fellow scientists has profound public health implications.  Through many lines of evidence, this body of research demonstrates a direct link between the antibiotic resistant bacteria on factory farms and antibiotic resistant bacteria in our food.

Of course, none of this is terribly surprising, is it? We’ve known since biblical times that flies are harbingers of disease. Included in the ten Biblical Plagues in the Book of Exodus is the Plague of Flies, which “came [as a] grievous swarm of flies into the house of Pharaoh, and into his servants’ houses, and into all the land of Egypt: the land was corrupted by reason of the swarm of flies.”

 However, when it comes to an issue as personal (and political) as food, we sometimes tend to forget unpleasant truths. In his book in Eating Animals, an acclaimed work of investigative journalism on the modern meat industry, Jonathan Safran Foer writes, “Food choices are determined by many factors, but reason (even consciousness) is generally not high on the list.” As hard scientific evidence accumulates on the link between antibiotic resistance on animal farms and public health, one can only hope growing consumer consciousness will force the meat industry to take a hard look at its practices.

1. Pew Campaign on Human Health and Industrial Farming

ResearchBlogging.org

Zurek, L., & Ghosh, A. (2014). Insects Represent a Link between Food Animal Farms and the Urban Environment for Antibiotic Resistance Traits Applied and Environmental Microbiology, 80 (12), 3562-3567 DOI: 10.1128/AEM.00600-14

 

 

3 thoughts on “From farm to table: insects as a conduit for antibiotic resistant bacteria

  1. Nick Stone

    Are any drug companies or government labs currently looking at phage therapy? My vague memory is that this is a complementary approach that petered out with the advent of broad-spectrum antibiotics – but if we really have picked all the low-hanging fruit in the antibiotic world, maybe it’s worth looking at again.

    • good question! as far as I know phage therapy never got much traction in the US as a popular treatment method, probably in part because it’s cheaper and simpler to mass produce an antibiotic that knocks out everything (phages are very specific to particular bacteria) and in part because the molecular tools to really develop phage therapy simply didn’t exist in the 1920’s and 30’s. However, using phages for gene therapy applications is, I believe, an area of active research.

      Another alternative I only recently heard about was the idea of designing nanobots that could target pathogenic bacteria with extreme precision. this still sounds a little science-fictiony to me, but if we run the antibiotic well dry in the next decade or so, nanite may end up being our best option.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s