Escherichia coli is implicated in the development and manifestation of host susceptibility to the roundworm Trichostrongylus colubriformis infections in sheep.

Applied breeding for host resistance to gastrointestinal nematodes represents a cost-effective strategy for parasitic control. While resistance is under moderate genetic influences, gut microbial components involved in the development of resistance or susceptibility remain largely unknown. Here we characterize the structure and metabolic potential of the proximal colon microbiota in unique ovine populations bred for resistance and susceptibility using a full-length 16S rRNA gene sequencing-based microbiome approach. The resistant lambs produced significantly fewer parasite eggs than susceptible animals grazing on the same pasture. Further, the resistant lambs displayed a significant reduction in worm establishment in response to a Trichostrongylus colubriformis challenge infection (P < 0.0001; N = 20 per group). Among 32 bacterial species or strains displaying a significant difference in relative abundance between the resistant and susceptible group, E. coli was more abundant in susceptible lambs. E. coli was also ranked as the most important species in distinguishing the resistant and susceptible status. Moreover, a microbial signature or balance consisting of E. coli (Numerator) and Parabacteroides distasonis and Bacteroides thetaiotaomicron (Denominator) predicted the resistance status with high accuracy. The metagenome function prediction also revealed that several pathways related to infectious diseases, such as Shigellosis and pathogenic E. coli infection, were significantly altered between the two phenotypes. Our findings demonstrated that microbial signatures with a high predictive power for the resistance status can be developed as biomarkers to facilitate the selection for host resistance in sheep.