Larvicidal activity ofBacillus thuringiensisvar.israelensisCry11Aa toxin againstHaemonchus contortus

Abstract

SUMMARYEffective control of gastrointestinal parasites is necessary in sheep production. The development of anthelmintics resistance is causing the available chemically based anthelmintics to become less effective. Biological control strategies present an alternative to this problem. In the current study, we tested the larvicidal effects ofBacillus thuringiensisvar.israelensisCry11Aa toxin againstHaemonchus contortuslarvae. Bacterial suspensions [2 × 108colony-forming units (CFU) g−1of the feces] ofB. thuringiensisvar.israelensisand recombinantEscherichia coliexpressing Cry11Aa toxin were added to naturallyH. contortusegg-contaminated feces. The larvae were quantified, and significant reductions of 62 and 81% (P< 0·001) were, respectively observed, compared with the control group. A 30 mL bacterial suspension (1 × 108CFU mL−1) ofB. thuringiensisvar.israelensisand recombinantE. coliexpressing Cry11Aa toxin were then orally administered to lambs naturally infected withH. contortus. Twelve hours after administration, feces were collected and submitted to coprocultures. Significant larvae reductions (P< 0·001) of 79 and 90% were observed respectively compared with the control group. The results suggest that the Cry11Aa toxin ofB. thuringiensisvar.israelensisis a promising new class of biological anthelmintics for treating sheep againstH. contortus.