Bacteria Associated with the Parasitic Nematode Haemonchus contortus and Its Control Using Antibiotics

Abstract

Internal parasitism, a significant cause of production losses in sheep, is routinely controlled by anthelmintic drenches. A better understanding and alternative control strategies are needed to combat the increasing resistance. This study investigated the presence of resident bacteria in the field strain of Haemonchus contortus. Adult female worms were collected from the abomasa of sheep. DNA was extracted from adult female worms and parasite eggs laid in vitro using long or shorter enzymatic incubation methods. Polymerase Chain Reaction (PCR) was performed using universal bacterial and phylum Firmicutes-specific primers; PCR products were cloned and sequenced. The analysis of the sequences shows a majority of the sequences belong to rumen bacteria, mainly Ruminococcus. Streptococcus was detected in four eggs, and adult worm samples and the sequences had a very high homology to the Streptococcus sequences in the database. Clostridium was detected only in the adult samples, whereas Nevskia and Pseudomonas were detected only in the egg samples. Three antibiotics, Ampicillin (Amp), Gentamycin (Gen) and Tetracycline (Tet), individually or combination, were tested to establish proof of concept that abomasal nematode parasites can be controlled by killing the resident bacteria. A larval migration inhibition assay was used to test the hypothesis. Tet (10 and 20 mM) resulted in around 30% mortality in larvae. Amp and Gen did not result in significant levels of larval mortality but, when given in combination, resulted in significant mortality of the larvae, suggesting the role of antibiotics in controlling the parasites by targeting the resident bacteria.