Suppression of Escherichia coli O157:H7 by Dung Beetles (Coleoptera: Scarabaeidae) using the lowbush blueberry agroecosystem as a model system

PLoS One. 2015 Apr 7;10(4):e0120904. doi: 10.1371/journal.pone.0120904. eCollection 2015.

Abstract

Wildlife as a source of microbial contamination is a food safety concern. Deer feces (scat) have been determined as a point source for Escherichia coli O157:H7 contamination of fresh produce. The ecological role of the scooped scarab (Onthophagus hecate (Panzer)), a generalist dung beetle species common in Maine blueberry fields, was explored as a biological control agent and alternatively as a pathogen vector between deer scat and food. A large-scale field survey of wildlife scat indicated that pathogenic E. coli O157:H7 was present, albeit at a low prevalence (1.9% of samples, n = 318), in the Maine lowbush blueberry agroecosystem. A manipulative field experiment verified that, should contact occur between deer scat and blueberry plants and fruit during the summer, contamination with E. coli O157:H7 can occur and persist for more than 72 h. For both the positive control and an experimental scat inoculation treatment, the levels of the bacterial population decreased over time, but at different rates (treatment x time interaction: F (1.9,18.8) = 358.486, P < 0.0001). The positive control inoculation, which resulted in a higher initial E. coli level on fruit, decayed at a faster rate than inoculation of fruit via scat in the experimental treatment. We conducted 2 laboratory studies to elucidate aspects of dung beetle feeding ecology as it relates to suppression of E. coli O157:H7 from deer scat to lowbush blueberry fruit. In both experiments, dung beetles buried the same amount of scat whether or not the scat was inoculated with the pathogen (F(1,6) = 0.001; P = 0.999 and (F (2,17) = 4.10, P = 0.147). Beetles feeding on E. coli inoculated deer scat were not found to vector the pathogen to fruit. In two studies, beetles lowered the amount of pathogenic E. coli persisting in soils compared to soils without beetles (F (2,9) = 7.757; P = 0.05 and F (2,17) = 8.0621, P = 0.004). Our study suggests that the dung beetle species, Onthophagus hecate, has the potential to contribute to the suppression of E. coli O157:H7 in agricultural landscapes.

MeSH terms

  • Agricultural Irrigation
  • Animals
  • Anti-Bacterial Agents / pharmacology*
  • Blueberry Plants / growth & development*
  • Blueberry Plants / microbiology
  • Coleoptera / microbiology*
  • Colony Count, Microbial
  • Ecosystem
  • Escherichia coli Infections / microbiology*
  • Escherichia coli Infections / prevention & control*
  • Escherichia coli O157 / pathogenicity
  • Feces / microbiology
  • Food Microbiology
  • Fruit / microbiology*
  • Models, Biological*

Substances

  • Anti-Bacterial Agents

Grants and funding

This research was supported by the Center for Produce Safety and the Maine Agricultural and Forest Experiment Station at the University of Maine with external publication number 3406. This work is based upon research supported in part by Hatch Grant number ME08562-10 from the USDA National Institute of Food and Agriculture. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.