Controlling gastrointestinal nematodes in cattle by Bacillus species

Abstract In this study, we tested the in vitro and in vivo larvicidal activity of Bacillus species against gastrointestinal nematodes in cattle, and their viability in the presence of anthelmintics. For in vitro tests, cattle feces naturally infected with trichostrongylides were incubated with spore suspensions of Bacillus circulans (Bcir), B. thuringiensis var. osvaldocruzi (Bto), B. thuringiensis var . israelensis (Bti) or B. thuringiensis var. kurstaki (Btk). Subsequently, residual larvae were counted and identified. All of the Bacillus species showed 60% or more larvicidal effects. Bcir and Bti were selected to be incubated with anthelmintics (moxidectin, nitroxynil and levamisole), and after 24, 72, and 144 h, their viability was evaluated. Bti showed highest drug resistance, maintaining a concentration of 1 × 10 7  CFU/mL. Based on this result, Bti was selected for in vivo tests on calves naturally infected with gastrointestinal nematodes. The calves were dived into four groups: Group 1, Bti suspension of ∼1 × 10 9  CFU orally administered; Group 2, Bti suspension of ∼1 × 10 9  CFU orally administered with levamisole (subcutaneously, 150 mg); Group 3, only levamisole (subcutaneously, 150 mg), and Group 4 untreated. Then 24 and 48 h after treatment, larvae numbers were counted. We observed a reduction of 84%, 100%, and 100% after 48 h of treatment, respectively, for Groups 1, 2 and 3 treatments in comparison with the untreated. The tested Bacillus species showed larvicidal activity against bovine trichostrongylides, and its association with anthelmintics. It may serve as a promising integrated alternative for control of gastrointestinal nematodes in cattle.