Investigation of Environmental Reservoirs of Strongyloides stercoralis as Targets for Utilising Nematophagous Fungi as Potential Biocontrol Agents

Author: Tara Garrard

Garrard, Tara, 2018 Investigation of Environmental Reservoirs of Strongyloides stercoralis as Targets for Utilising Nematophagous Fungi as Potential Biocontrol Agents, Flinders University, College of Science and Engineering

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This thesis presents an investigation into the environmental reservoirs of Strongyloides stercoralis in Australia and aimed to develop methods to reduce numbers of infective larvae in these areas as part of an integrated multifaceted approach to control the parasite.

This work develops a framework for further investigations into a neglected human parasite in an Australian context using native fungi to reduce larval loads in environmental reservoirs. This was conducted by attempting to develop a real-time PCR assay for larval detection in environmental samples, the subsequent aims were to isolate native nematophagous fungi from Northern Territory soils, assess nematophagous efficacy in faecal-soil matrices and assess the toxicity of nematotoxins from nematophagous fungi on Strongyloides ratti.

This work investigates the limitations of working with an organism that is prevalent in remote and isolated areas with limited access to samples. Sample storage and transit methods require development to improve DNA yields and numbers of viable organisms as these were a distinctive constraint in the study.

Soil samples were collected from the Northern Territory in Australia and the sprinkle plate used as the technique to isolate potential nematophagous fungi. Characterization of the isolates proved difficult due to the lack of clarity between predatory activity, saprotrophic activity and weak predatory activity. It was concluded that none of the isolates were strictly nematophagous fungi and were weakly or opportunistically predating nematodes

Predatory activity of nematophagous fungi has been attributed to both biological competition and induced by low nutrient substrates. S. stercoralis are known to occur in soil-faecal matrices, therefore this work aimed to assess the efficacy of nematophagous fungi in these substrates. A. oligospora and C. elegans were used as indicator organisms in a soil-faecal matrix. A. oligospora demonstrated the ability to effectively trap and remove 99.9% of C. elegans in a canine faecal matrix, however, in a soil-faecal matrix trapping efficacy was only 61.2%. Providing clarity on the potential applicability of nematophagous fungi to control nematodes in high nutrient substrates.

The nematotoxic substances produced by P. ostreatus, P. ostreatus var. columbinus and H. clelandii, which aid in their nematophagous processes were investigated for their toxicity to C. elegans and S. ratti. The purpose of this work was to identify if extracts had potential for use as an environmental control measure for free-living S. stercoralis larvae. These extracts proved effective at immobilising C. elegans larvae but the toxicity towards S. ratti was inconclusive.

This research is one of very few studies investigating the effect of fungi on S. stercoralis and provides a framework for more directed research in this area.

Keywords: Strongyloides stercoralis, biological control, nematophagous fungi

Subject: Environmental Science thesis

Thesis type: Doctor of Philosophy
Completed: 2018
School: College of Science and Engineering
Supervisor: Professor Howard Fallowfield