A Nematode Crude Extract Acts as an Elicitor of the Nematocidal Activity of Nematophagous Fungi Liquid Culture Filtrates Against Haemonchus contortus (Nematoda: Trichostrongylidae)

Aim This study was designed to investigate if culturing nematophagous fungi (NF) in the presence of a Haemonchus contortus larva crude extract ( Hc CE) enhances the nematocidal activity of nematophagous fungi liquid culture filtrates (NFCF). Materials and Methods Four NF Arthrobotrys oligospora , A. musiformis , Duddingtonia flagrans and Clonostachys rosea were cultured in flasks ( n = 5) containing Czapek-Dox broth medium (CDB) in the presence or absence of Hc CE. NFCF recovered by filtration of each fungus (200 mg/mL) were assessed on H. contortus infective larvae (L3) using 96-well micro-titer plates ( n = 4). Additionally, CDB and water were considered negative controls, while Ivermectin acted as a positive control. After 48 h confrontation, ten 10-μL aliquots of each well were deposited on slides and observed under the microscope (40 ×). Dead and alive larvae in the aliquots were quantified, and a mortality rate (MR) was estimated. Results The MR of the different NFCF was greatly enhanced by the presence of Hc CE. The four NF incubated in the absence of Hc CE showed low mortality percentages from 8.2 to 25.8%; in contrast, when the assessed NF growth in the presence of Hc CE showed a lethal activity ranging from 66.8 to 80.5%. Only C. rosea showed a moderate increase in the presence of the elicitor (42.7%). Conclusion This study shows evidence about the Hc CE enhances the production of nematocidal activity in NFCF. Future studies should be performed to elucidate the compounds responsible of the nematocidal activity that could have important implications in the control of sheep haemonchosis. Graphical Abstract