Dung Beetles and Soil Bacteria Promote Food Safety.

Jones MS, Fu Z, Reganold JP, Karp DS, Besser TE, Tylianakis JM & Synder WE (2019) Organic farming promotes biotic resistance to foodborne pathogens. Journal of Applied Ecology. DOI: 10.1111/1365-2664.13365

 

Foodborne Outbreaks

In recent months you may have noticed headlines concerning what foods to avoid. Not because of some fad new diet, but because of foodborne illness. Recently there was a recall in six states for avocados affected by listeria bacteria. Prior to that there was an outbreak of E. coli in romaine lettuce.

Beyond the headlines, the majority of our produce is safe. Farmers, transporters and stores do a fairly good job at maintaining safe produce. However, limiting any possibility of contamination is always something to strive for and produce is susceptible to pathogens at pretty much every step of the way, even while they are still growing!

Escherichia coli (E. coli) naturally occurs in our stomachs as well as in most animals’ stomachs. Occasionally bad strains of the bacteria can spread via fecal matter (poop!). Farms are a full of delectable resources that many wildlife find desirable and are often attracted to such places. In order to dissuade visitations of wild animals that may infect produce with E. coli-enriched fecal matter, commercial farmers eliminate landscape heterogeneity and potential wildlife habitat by removing habitats like hedgerows and ponds.

 

How Resistant is Commercial vs. Organic Farming?

Preventative measures like limiting heterogeneity and pesticides have been utilized by many commercial fields. But how effective is it at eliminating potential pathogens? A team of scientists led by Matthew Jones were interested in how resistant differ types of farming practices are to foodborne pathogens.

The team sampled 70 broccoli fields across the US west coast with both field and laboratory experiments. The farming practices were those that used commercial farming methods, organic methods, or integrated methods in which the farm grew organic vegetables and also raised livestock. In the field, the team was interested in how quickly fecal matter breaks down. Within each field, the team placed boar feces adjacent to growing broccoli. These feces were not infected with any pathogens; however, the feces represented a potential pathway (via wildlife) for pathogens to infect the broccoli. In addition, the team also conducted laboratory experiments to understand how the presence and diversity of dung beetles and soil bacteria can aid in the breakdown of E. coli-infected pig feces mixed with soils. The team chose to examine boar feces in the field and pig feces in the lab because they are closely related species that represent potential wildlife and livestock interactions on many of these farms.

By looking at the breakdown of feces in the field and how beetles and bacteria breakdown infected feces in the lab, the team hoped to understand: 1) how quickly do different farming practices breakdown fecal matter and 2) how do different farming practices alter the biodiversity of communities that breakdown fecal matter.

Irrigated farming in Salinas, California. Source: Wikimedia
Maybe Another Reason to Farm Organic

The team found that the soil bacteria did differ among the farms sampled. Bacterial diversity was greatest in organic farms!

The most likely driver of bacterial diversity was the type of farming system used (commercial, organic, or integrated organic) as well as the amount of organic matter in the soil. Both organic and integrated organic farms had higher percentages of organic matter, which may in part be because of the cover crop diversity and application of animal manure; both of which aren’t used in commercial farming practices.

Dung beetle diversity increased in organic farms as well. These critters were capable of removing over 90% of the total animal waste in a matter of days! Simply by maintaining a diverse population of beetles and soil bacteria, pathogens like E. coli could virtually be eliminated in farms and potentially our food!

Why Biodiversity Matters

At the end of the day we, as consumers, are most concerned about food safety. Previous food regulations have linked farms rich in biodiversity (often organic rather than commercial farming) are at greater risk of crop contamination. But that may not be entirely the case. Findings from Jones and colleagues found that farms with a greater diversity in beetles and bacteria were actually more efficient at eliminating E. coli.

By having a more diverse farm or ecosystem, there are more checks and balances. High biodiversity creates a more stable environment. Think of these beetles and soil bacteria as a natural pesticides!

 

Onthophagus Taurus, the bull-headed beetle. One of the most abundant dung beetles observed during the field study. Source: imgur
Conclusion

Outbreaks of pathogens in our foods can happen. However, Jones and colleagues’ findings suggest that there may be more to food safety than eliminating variables from the natural environment through pesticides and removing wildlife habitat. Having a rich diversity in beetles and soil bacteria may enhance the safety of our food and our health.

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Aidan Barry

I am truly fascinated by our ever-changing world, from ecosystems to the interstitial cracks. I'm currently earning my Master's in Natural Resources from the University of Connecticut. My research is focused on how sea-level rise and restoration strategies alter carbon cycling and microbial communities in salt marshes. When I'm not in the lab or covered in marsh muck, there's a good chance I'm down at the beach surfing, up in the mountains backpacking, or performing music somewhere in between. Instagram: aidanbarry94

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