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

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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

 

 

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Probing the Aerosol Microbiome of New York City’s Subway System

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River of "psychomagnotheric slime" in the NY subway from the Ghostbusters game for Wii.

River of “psychomagnotheric slime” in the NY subway from the Ghostbusters game for Wii.

If you’re a sci fi geek like me, you’ve almost certainly consumed some form of media that features perilous encounters in the New York City subway system (our AI oppressors in The Matrix, giant genetically engineered cockroaches in Mimic, negatively charged slime in Ghostbusters, lots and lots of villains in Teenage Mutant Ninja Turtles….I could go on). In reality, any non-human dangers that do exist in the subway are likely to be more insidious than the large, charismatic monsters featured by Hollywood. Do the microorganisms inhabiting subterranean bowels of New York pose any real threat? If a dangerous epidemic were to hit the metropolis, would it spread above ground or propagate below?

While zombie viruses may be a bit far-fetched, the possibility of a pathogen propagating through heavily-trafficked subway is not

While zombie viruses may be a bit far-fetched, the possibility of a pathogen propagating through the heavily-trafficked subway is not

Motivated by these sorts of public-health questions, a team of medical microbiologists led by Dr. Norman Pace at the University of Colorado, Boulder, decided to investigate the airborne microorganisms inhabiting the NYC subway. Historically, the regulatory focus on city air quality has addressed particulate materials (soot) and chemicals.  Comparably little attention is paid to the airborne microbes and other biomaterials to which we are regularly exposed. However, in heavily-trafficked public locations like the subway (with a ridership exceeding 1.5 billion per year!), airborne pathogens may represent a much greater danger than chemical pollutants.

For  nearly two years, Dr Pace and his team collected “bioaerosols” on seven NYC subway platforms and three neighboring above-ground sites, using a device known as a fluid impinger- essentially a fancy vacuum that sucks up and filters air, trapping bacteria-sized particles. They used a combination of molecular techniques to determine the genetic composition of subway bacterial communities.

Their diagnosis? Breathe easy! There appears to be no imminent danger posed by subway air. The subway microbiome is relatively simple and homogenous, both throughout the system and over time. A mere 26 taxa comprise over 75% of the bacterial populations found in the study, as compared with the millions or billions of taxa found in more diverse environments such as soils. The dominant subway species, much like their aboveground counterparts, are a mixture of bacteria characteristic of soil, water and human skin, all relatively harmless. [A fun aside: it turns out the leading mechanism by which microbes are transferred from skin to air is through heat convection! Our body temperatures are typically greater than the surrounding air, meaning we emit a constant plume of heat carrying components of our skin microbiome]

The remarkable similarity between the microbial communities of subway air and aboveground city air is testament to a highly effective air circulation system known as “passive train pumping”. It’s the same system that causes the rush of air you feel when walking over a subway grate. According to Dr. Pace, the uniformity of microbial communities throughout the subway indicates passive train pumping is doing a good job replenishing the subway with fresh air.

PathoMap, a Weil Medical School based effort to develop a map of the New York City microbiome for pathogen monitoring and predictions

PathoMap, a Weil Medical School based effort to develop a map of the New York City microbiome for pathogen monitoring and predictions

Subway microbiome research represents one component of a larger research effort known as PathoMap. Led by  Dr. Chris Mason and his lab of microbiologists at Weil Cornell Medical School in New York, PathoMap aims to use new DNA sequencing technologies to establish “pathogen weather maps” of the city. The research group collects regular environmental samples from highly trafficked regions of NYC for microbial profiling. Microbial genomic profiles are then spatially mapped using GIS-based tools. Ultimately, Dr. Mason hopes that his maps, which track the genetic dynamics of the city’s microbiome,  will be used to detect and respond to microbial dangers, thus reducing the spread of pathogens.

The original article can be found here.