Bacillus spp. toxicity against Haemonchus contortus larvae in sheep fecal cultures

The gastrointestinal nematode Haemonchus contortus is a major productivity constraint in sheep. In this study, the nematicidal effects of Bacillus circulans, Bacillus cereus, Bacillus thuringiensis var. israelensis, Bt. var. osvaldocruzi, Bt. var. morrisoni, and Bt. var. kurstaki were assessed in free-living larval stages of H. contortus. A spore-crystal suspension containing approximately 2 × 108 UFC/mL of each strain was added to sheep feces that were naturally infected with H. contortus eggs, and the presence of larvae was then evaluated. We observed a significant (p > 0.05) reduction in larval development when using B. circulans, B. thuringiensis var. israelensis, Bt. var. osvaldocruzi and Bt. var. kurstaki, and these effects were proportional with the amount of bacteria added to the feces. However, no effect was observed when Bt. var. morrisoni or B. cereus was added. These observations suggest that these bacteria might be effective as nematicides and may allow for the development of integrated biological control of zooparasitic nematodes.

Highlights► Bacillus strains were screened for activity against the larval stages of Haemonchus contortus. ► Larvicidal effects occur by the vegetative and spore-crystal stages. ► Bacillus can be used as alternative biocontrol for important veterinary nematode.