Larvicidal activity of Bacillus circulans against the gastrointestinal nematode Haemonchus contortus in sheep.

Efficient control of gastrointestinal parasites is necessary in sheep breeding. However, the available chemically based anthelmintics are becoming less effective due to the development of parasite resistance. An alternative to this problem is biological control. In the present study, we tested the larvicidal effect of Bacillus circulans by administering a spore suspension (2 × 109 colony forming units/ml) orally to lambs naturally infected with Haemonchus contortus. The number of faecal larvae was quantified daily and a significant reduction (~87%, P< 0.05) of larval development was observed after administration of B. circulans. Using a transformed B. circulans with green fluorescent protein, we were able to detect B. circulans in the faeces at 4 h post-administration and 72 h after cessation of its administration. These results suggest the use of B. circulans as a promising biological alternative for parasite control.