Study rebuts pesticide lobby claims that organic farms are more likely to harbour disease-causing bacteria

Organic farming promotes natural resistance to common foodborne human pathogens, according to a study that evaluates the benefit of soil organisms. The new study is featured in a blog post on the Beyond Pesticides website.

The new study adds to an existing body of evidence showing the falsehood of claims by pesticide defenders like Dennis Avery of the Hudson Institute to the effect that organic food is more dangerous to eat due to foodborne pathogens.

The new study found that organic farming systems naturally act to clean up and decompose potentially pathogen-bearing animal faeces by protecting valuable species of dung beetles and soil bacteria. While these natural systems suppress pathogens on organic farms, conventional chemical-intensive farms are left with higher levels of faecal residues and are therefore significantly more likely to yield produce carrying such foodborne pathogens as E. coli. The authors emphasize that curbing the spread of common foodborne pathogens could save thousands of lives and prevent millions of illnesses each year.

The study, “Organic farming promotes biotic resistance to foodborne human pathogens", published in the Journal of Applied Ecology, compares dung beetle populations, soil bacteria diversity, and faeces removal rates on 70 organic and conventional broccoli farm fields across the west coast of the US. In addition to studying field conditions, authors conducted microcosm studies to directly test the effects of dung beetles and soil microbes on the suppression of introduced E. coli.

Results from field analyses show that organic management practices lead to greater biodiversity among dung beetles and soil microbes, which translate to higher rates of faeces removal. Microcosm results confirm that by removing faecal matter, the beetles and microbes retained by organic management reduce potential E. coli contamination. Beyond Pesticides comments, "These new findings add to the list of ecosystem services unique to organic farms, further bolstering the case for organic as not only an ecological but an economical solution to global food production."

Beyond Pesticides says that in the context of recently reviewed insect declines worldwide, this study also serves as a warning of yet another key ecosystem service that will certainly be lost unless a major agricultural transformation to organic systems is mobilized. Dung beetles, whose actions in soils not only protect against pathogens, but also unlock critical nutrients, are in decline. The impacts of dung beetles on soil fertility are vital to the sustainability of farms and pastures used to maintain livestock. By burying and processing faeces on cattle farms, dung beetles introduce 80% more nitrogen into the soil than would otherwise remain. By increasing soil organic matter, dung beetles simultaneously increase water infiltration, thus stabilizing farms and heavily grazed areas against erosion, flooding, and drought.

Findings from the new study highlight the need for dung beetle diversity in addition to abundance, since some dung beetles bury faeces more effectively than others. Notably, researchers find that the commonly introduced species O. nuchicornis, which tends to dominate over other species and reduce overall diversity, is less effective at burying faeces, with consequences for both E. coli contamination and soil fertility. Similarly, previous work attests to the importance of soil microbial diversity for maintaining ecosystem services. The key to healthy produce and fertile soils, across the board, is diversity.

Due to agrochemical use, that precious diversity is in decline. Monitoring in Europe, according to the 2019 review of insect declines, shows the greatest terrestrial loss of insect biodiversity on record to date: more than 60% of documented dung beetle species are in decline. Soil microbial diversity, too, is threatened by continued application of pesticides in industrialized agriculture. Highly toxic gases known as “soil fumigants” are used on a wide range of high-value crops to control nematodes, fungi, bacteria, insects, and weeds. Soil fumigants wipe out entire soil communities, thus necessitating the use of other chemicals  to provide the fertility and pest control services that soil  organisms provide. In addition to fumigating soil, which intentionally kills all living things in the soil, other chemical-intensive practices also threaten soil  life. Glyphosate, the most widely used herbicide, is also an antibiotic. Glyphosate-tolerant plants release glyphosate into the soil, where it has a continued impact on soil microbial diversity.

Beyond Pesticides comments, "These patterns carry a lesson. Insects and microbes that act to control crop pests and fertilize the soil reduce the need for pesticide and chemical fertilizer use. Reliance on chemical controls creates a vicious treadmill: pesticide use kills natural agents of pest control, thus creating a demand for more pesticide use, which kills more of the beneficial organisms, and so on."

Sources: Beyond Pesticides and Journal of Applied Ecology (see below)
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Organic farming promotes biotic resistance to foodborne human pathogens
Matthew S. Jones, Zhen Fu, John P. Reganold, Daniel S. Karp, Thomas E. Besser, Jason M. Tylianakis, William E. Snyder
Journal of Applied Ecology 2019;1–11.
Accepted: 10 December 2018
DOI: 10.1111/1365-2664.13365

Abstract

1. Farmland biodiversity benefits pollination, biological control and other key ecosystem services. Food safety has been seen as an exception to this broader pattern, as diverse farmlands attract wildlife that vector foodborne human patho- gens. Resulting mitigation efforts thus often seek to deter wildlife by removing natural habitats, while also excluding vertebrate livestock. However, surprising recent evidence suggests that farm simplification actually increases the likelihood that produce will be contaminated with human pathogens.
2. Here, we consider the possibility that intensified agriculture harms faeces-feeding (coprophagous) beetles and bacteria, which could contribute to heightened food- safety risk. In 70 commercial vegetable fields spanning the US west coast, using either organic or conventional farming methods, we surveyed coprophages both above- and below-ground. We also measured removal rates of the faeces of Sus scrofa, which vectors foodborne pathogens both as livestock and as feral wildlife.
3. Above-ground, organic farms fostered dung beetle species that removed S. scrofa faeces more rapidly than was seen on conventional farms, although this benefit was weakened in simplified landscapes dominated by pasture and an introduced dung beetle. Below-ground, organic farming encouraged significantly higher bio- diversity among soil bacteria. Organic farming similarly benefitted dung beetles and bacteria on farms that produced livestock alongside vegetables, or vegetables alone.
4. Complementary laboratory experiments revealed that the dung beetle species and biodiverse bacterial assemblages typical of organic farms were significantly more effective at suppressing human-pathogenic Escherichia coli O157:H7, com- pared to coprophage communities associated with conventional farms. This sug- gests that farm management practices, coprophage conservation, and human–pathogen suppression might be linked.