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

 

 

Combing sloth hair for rainforest fungi, scientists uncover anti-malaria, anti-cancer and antibiotic activity

Standard

Hosting the highest biodiversity of any biome on Earth, tropical rainforests may represent a goldmine of “bioactive” compounds- medicinal chemicals produced naturally by plants, insects and microorganisms. Given a full 50% of all medicines introduced between 1981 and 2006 came directly from nature, the notion of “bioprospecting”, or combing the diversity of tropical forests for new drugs, has enticed imaginations for decades. But Big Pharma’s interest in bioprospecting has waned in recent decades due to the slow pace of discovery. However, hope is still alive amongst microbiologists working in the field.  And for good reason. In a study published last week in the journal PLOS ONE, scientists report on a new, highly promising source of bioactive compounds from a rather unusual suspect: the three toed sloth.

Sloths are famous for their green coloration, a result of the algae that live in their hair and help provide camoflauge

Sloths are famous for their green coloration, a result of the algae that live in their hair and help provide camoflauge

Sloths host entire ecosystems in their thick, coarse hair, including plants (green algae), arthropods (cockroaches, moths and roundworms), bacteria and fungi. Microbiologist Sarah Higgingbotham at the Smithsonian Tropical Research Institute in Panama was interested in finding out whether any of this diversity was medicinally valuable. Of particular interest to Higgingbotham and colleagues were the numerous species of fungi living in sloth hair. Fungi have made substantial contributions to the pool of natural drug products since the discovery of penicillin over 80 years ago.

Fungi are a diverse kingdom of organism from which have come a variety of natural products, including food supplements, antibiotics such as penicillin, and anti-cancer agents.  Credit: National Geographic

Fungi are a diverse kingdom of organisms that produce a variety of economically valuable compounds, such as antioxidants, antibiotics and anti-cancer agents.
Credit: National Geographic

To uncover potential drug-producing fungi, Higgingbotham and colleagues collected samples of the coarse, outer hair from nine unsuspecting three toed sloths found moseying along a road in Soberanía National Park, Panama (yes, aspiring microbiologists, this is something you can actually get paid to do). The hair samples were taken back to their lab, incubated on petri dishes, and checked regularly for fungal growth. Following growth, the researchers collected fungal hyphae from the plates, extracted and sequenced their DNA in order to determine identity. In total, 84 unique fungi were isolated. Although these fungi are a highly diverse group, including several potentially novel species, most fell into the taxonomic class Sordariomycetes – a well documented source of bioactive compounds.

Samples of 70 isolated fungal strains were grown in liquid culture media and tested for “bioactivity” against malaria, Chagas disease and the breast cancer cell line MCF-7, in addition to 15 human pathogenic bacteria. A strain was considered “highly bioactive” if it inhibited growth of a disease by 50% or more. For 50 of these strains, the researchers also constructed “antibiotic activity profiles” – scorecards indicating the degree to which a given fungal strain inhibits a range of bacterial pathogens. Antibiotic activity profiles are commonly used in medicine to determine the efficacy of a particular drug against an infection. Creating antibiotic activity profiles allows scientists to compare novel antibiotics to databases of antibiotics currently on the market and identify new disease-fighting drugs.

Malaria parasite P. falciparum eats its way through the hemoglobin in red blood cells.  Credit: National Geographic

Malaria parasite P. falciparum eats its way through the hemoglobin in red blood cells.
Credit: National Geographic

Overall, two of the fungal isolates were highly bioactive against the malaria parasite Plasmodium falciparum and eight were active against the Chagas parasite Trypanosoma cruzi. Fifteen fungal isolates were highly active against the MCF-7 cell line. Bioactivity against T. cruzi is particularly rare and represents a promising alternative to the two currently used drugs, nitrofurane and benznidazole, both of which can have toxic side effects.

Twenty of the fifty fungal isolates screened were bioactive against at least one bacterial pathogen. An exceptionally promising isolate, Lasiodiplodia sp.1, aggressively reduced the growth of several pathogenic Gram-negative bacteria. Infections caused by multi drug-resistant (MDR) Gram-negative bacteria, such as E.coli and Pseudomonas aeruginosa, are on the rise worldwide due to the overuse of antibiotics in hospitals and clean rooms. There is currently a paucity of drugs in development against MDR Gram-negative bacteria compared with their Gram-positive counterparts. Lasiodiplodia’s bioactivity profile did not match that of any known antibiotics, suggesting a potentially novel disease-fighting mechanism.

What do hospital clean rooms and factory farms have in common? Both use lots of antibiotics, leading to an increase in multidrug-resistant bacteria

What do hospital clean rooms and factory farms have in common? Both use lots of antibiotics, leading to an increase in multidrug-resistant bacteria

Twenty nine of the fungal strains isolated by Higgingbotham and colleagues are known endophytes– fungi that make a home living on plants. Endophytic rainforest fungi have recently made news for other remarkable metabolic features such as the capacity to metabolize plastic . The discovery of endophytic fungi on sloth hair increases our understanding of the habitat range occupied by these diverse organisms. Higgingbotham speculates some her fungi living may be associated with the algae present in sloth hair, forming a symbiosis analogous to that seen in lichen.