Metagenetic Analysis of the Pregnant Microbiome in Horses

Abstract

Placentitis is the leading cause of infectious abortion in the horse. Additionally, it can result in weak and/or growth restricted offspring. While the etiology of ascending placentitis is well described in mares, less is known regarding the pathogenesis of other types, such as nocardioform placentitis. This study aims to identify the microbial communities in different body sites of the pregnant mare in early gestation to establish a core microbiome that may be perturbed in pathologic pregnancies such as placentitis. We hypothesize that the equine placenta harbors a distinct resident microbiome in early pregnancy when characterized by metagenetics and that there will be a disparity in bacterial communities from the oral, vaginal, and fecal microbiome. Samples were collected from the oral cavity, vagina, anus, and the allantoic portion of the allantochorion (“placenta”) from five pregnant mares between 96 and 120 days of gestation. The V4 region of the 16S rRNA gene was amplified for Illumina MiSeq sequencing to examine core bacterial communities present in the different body sites. Microbial community composition of the pregnant ponies by body site was significantly different (Bray–Curtis dissimilarity). The placenta was significantly different from the feces, oral cavity, and vagina. Alpha diversity measuring the Shannon diversity matrix was significant, with the body sites being a compounding variable, meaning there was a difference in richness and evenness in the different microbial communities. Feces had the greatest alpha diversity, while the oral cavity and placenta similarly had the least. In conclusion, metagenetics did reveal distinct community differences in the oral, fecal, vaginal, and placenta cavities of the horse. The equine placenta does show similarities in its microbial communities to the oral cavity. Further research needs to be completed to investigate how bacteria may be translocated to the placenta from these other body sites and how they contribute to the development of placentitis.

Genome Sequence Comparisons between Small and Large Colony Phenotypes of Equine Clinical Isolates of Arcanobacterium hippocoleae

“…Despite the isolation of A. hippocoleae from the reproductive tract of mares with some related health issues [ 1 , 2 , 3 , 4 , 5 , 6 ], the significance of the bacterium as a commensal, primary, or opportunistic pathogen has not been established. The genus Arcanobacterium was detected in 16S rRNA gene sequence-based metagenomic studies with low relative abundance from the uterus and vagina of healthy mares [ 7 , 9 , 11 ]. However, metagenomic techniques that provide species-level information are required to confirm whether A. hippocoleae is part of the normal microbial ecology of the genital tract of mares.…”

“…Understanding the role of A. hippocoleae as a commensal in the microbiome of the mare’s genital tract or its significance as a pathogen is very important. Currently, there are only a few metagenomic-based reports available focusing on the reproductive system of mares [ 7 , 8 , 9 , 10 , 11 ]. However, all these studies were based on 16S rRNA gene sequencing, and their resolutions were only up to the genus level.…”