The bacterial community associated with the sheep gastrointestinal nematode parasite Haemonchus contortus

Abstract

Culture-independent methods were used to study the microbiota of adult worms, third-stage larvae and eggs, both in faeces and laid in vitro, of Haemonchus contortus, a nematode parasite of the abomasa of ruminants which is a major cause of production losses and ill-health. Bacteria were identified in eggs, the female reproductive tract and the gut of adult and third-stage larvae (L3). PCR amplification of 16S rRNA sequences, denaturing gradient gel electrophoresis (DGGE) and clone libraries were used to compare the composition of the microbial communities of the different life-cycle stages of the parasites, as well as parasites and their natural environments. The microbiomes of adult worms and L3 were different from those in the abomasum or faeces respectively. The H. contortus microbiota was mainly comprised of members of the phyla Proteobacteria, Firmicutes and Bacteroidetes. Bacteria were localised in the gut, inside eggs and within the uterus of adult female worms using the universal FISH Eub338 probe, which targets most bacteria, and were also seen in these tissues by light and transmission electron microscopy. Streptococcus/Lactococcus sp. were identified within the distal uterus with the probe Strc493. Sequences from the genera Weissella and Leuconostoc were found in all life-cycle stages, except eggs collected from faeces, in which most sequences belonged to Clostridium sp. Bacteria affiliated with Weissella/Leuconostoc were identified in both PCR-DGGE short sequences and clone libraries of nearly full length 16S rRNA bacterial sequences in all life-cycle stages and subsequently visualised in eggs by fluorescent in situ hybridisation (FISH) with group-specific probes. This strongly suggests they are vertically transmitted endosymbionts. As this study was carried out on a parasite strain which has been maintained in the laboratory, other field isolates will need to be examined to establish whether these bacteria are more widely dispersed and have potential as targets to control H. contortus infections.

Helminth Microbiomes – A Hidden Treasure Trove?

“…Wolbachia, which has become the target of intense investigations aimed to develop novel filaricidal compounds [14][15][16][17][18]. This evidence supports the hypothesis, strongly corroborated by recent experimental findings [19,20], that the digestive system as well as other organs and tissues of GI nematodes may also harbour resident microbes with essential roles in parasite physiology and survival. Fully characterizing and understanding the structure and function of helminth microbiomes, and determining the role/s they play in key aspects of parasite biology and host-parasite interactions, could not only have broad implications for future studies of the origin of parasitism itself, but might also lead to the discovery of radically new interventions against these worms.…”

“…For GI nematodes, experimental evidence of microbiome acquisition strategies is available for two species, namely Haemonchus contortus, an abomasal roundworm of small ruminants [19] and Trichuris muris, a large intestinal whipworm of rodents [20] (cf. Figure 1).…”

“…Figure 1). For the former, a recent study [19] localised selected genera of bacteria (i.e. Weissella and Leuconostoc) to the gut of adult worms and to the uterus of sexually mature females by fluorescence in situ hybridization (FISH) and transmission electron microscopy; using DNA fingerprinting, the same genera could be identified in eggs laid by these females and, following larval culture, their L3 offspring [19].…”

“…For the former, a recent study [19] localised selected genera of bacteria (i.e. Weissella and Leuconostoc) to the gut of adult worms and to the uterus of sexually mature females by fluorescence in situ hybridization (FISH) and transmission electron microscopy; using DNA fingerprinting, the same genera could be identified in eggs laid by these females and, following larval culture, their L3 offspring [19]. Notably, these microorganisms could not be identified in the faecal matter on which larval culture was performed, thus providing evidence of maternal transmission of these bacteria [19].…”

Ruminal fermentation, microbial population and lipid metabolism in gastrointestinal nematode-infected lambs fed a diet supplemented with herbal mixtures

“…Gastrointestinal parasitic infections is one of the major issues impacting the health of livestock animals, especially by the most pathogenic gastrointestinal nematode (GIN) parasite Haemonchus contortus. This GIN sucks abomasum blood and causes anemia, reduces reproductive capacity and animal production, resulting in considerable economic losses [1,2]. Since GIN reduces productivity, infected animals require more resource input to achieve the same level of productive output compared to the non-infected animals.…”