Can human pathogens be reduced by dung beetles and soil bacteria?

Can human pathogens be reduced by dung beetles and soil bacteria?
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Published in the Journal of Applied Ecology, research encourages dung beetles and soil bacteria at farms as they could naturally suppress human pathogens.

Food safety regulations increasingly pressure growers to remove hedgerows, ponds and other natural habitats from farms to keep out pathogen-carrying wildlife and livestock. However, this could come at the cost of biodiversity. But now research is encouraging the presence of dung beetles and soil bacteria at farms as they naturally suppress E. coli and other harmful human pathogens.

Preventing human pathogens from spreading

Matthew Jones, who led the research as part of his PhD project at Washington State University, USA, said: “Farmers are more and more concerned with food safety. If someone gets sick from produce traced back to a particular farm it can be devastating for them.”

“As a result, many remove natural habitats from their farm fields to discourage visits by livestock or wildlife, making the farmland less hospitable to pollinators and other beneficial insects or birds”, he added.

Currently, we know that dung beetles bury faeces below ground and make it difficult for pathogens to survive, but researchers aimed to find out just how effective this may be.

Details of the study

To study how this may aid food safety, the entomologist drove a van full of pig faeces along the US West Coast to follow the planting of broccoli at 70 farm fields during the growing season. Broccoli, much like leafy greens, is susceptible to faecal contamination due to its proximity to the ground and the likelihood of humans consuming it without cooking.

The pig faeces were used to attract dung beetles and observe how quickly they would clean up. The experiment was carried out at conventional and organic farms, and farms with or without livestock.

“We found that organic farms generally fostered dung beetle species that removed the faeces more rapidly than was seen on conventional farms”, said Professor William Snyder of Washington State University.

Dung beetles likely kill harmful bacteria when they consume and bury the faeces. Previous research also suggested that these beetles have antibiotic-like compounds on their body.
Validating the research with human pathogens

To validate these findings, the researchers exposed the three most common species found in the field survey to pig faeces contaminated with E. coli. A 7-day laboratory experiment revealed that Onthophagus taurus and Onthophagus nuchicornis, both of which bury faeces as part of their breeding behaviour, reduced E. coli numbers by > 90% and < 50% respectively.

Higher biodiversity was encouraged by organic farming among soil bacteria, which decreased the survival of pathogens.

“Bacteria are known to poison and otherwise fight among themselves and the same may be happening here”, explained Snyder.

Promoting plant and insect diversity

These results suggest dung beetles and soil bacteria may improve the natural suppression of human pathogens on farms, making a case for reduced insecticide use and the promotion of greater plant and insect diversity.

“Wildlife and livestock are often seen as something that endanger food safety, but our research shows that reducing on-farm biodiversity might be totally counterproductive”, Jones concluded.

“Nature has a ‘clean-up crew’ of dung beetles and bacteria that quickly remove faeces and the pathogens within them, it appears.

“So, it might be better to encourage these beneficial insects and microbes.”

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