Microbial Profiling of Amniotic Fluid, Umbilical Blood and Placenta of the Foaling Mare

Abstract

The presence of a microbiome/microbiota in the placenta is hotly debated. In previous studies, the presence of bacteria in equine amniotic fluid and umbilical blood was independent of foal health. The objective of the present study was to determine if the same bacteria are present in the equine placenta as in amniotic fluid and umbilical blood. Samples were obtained from 24 parturient mares and foals. Placental bacterial DNA was extracted, and the microbiome was identified using 16S rRNA sequencing. All amniotic fluid samples contained some polymorphonucleocytes; bacteria were isolated from four samples. Aerobic or anaerobic growth was found in 18 and 3 umbilical blood samples, respectively. Serum amyloid A was <5 mg/L in all 24 samples, total WBC varied between 2900 and 10,700/µL, and fibrinogen varied between 0 and 5.16 g/L. In jugular blood, serum amyloid A was <5 mg/L in all 24 foals, total white blood count was 3200 to 8100/µL, and fibrinogen was 0.44 to 4.42 g/L. The diversity of bacterial microbiota was similar in all placental regions at the phylum level but differed at the genus level; the most abundant phyla were Proteobacteria (42–46.26%) and Actinobacteria (26.91–29.96%). In conclusion, bacteria were found in the fetal compartments and placenta of healthy equine pregnancies; however, we can neither prove nor disprove the hypothesis that the placenta has its own microbiome.

The dogma of the sterile uterus revisited: does microbial seeding occur during fetal life in humans and animals?

“…This research suggested an association between placental and extraplacental (maternal oral and vaginal) microbiomes. More recently, Hemberg et al (2023) sampled the placenta after expulsion through the vaginal canal, targeting three different areas of the organ (i.e. the cervical star, the umbilical cord at the attachment of the amniotic sac, and the mid-part of the pregnant horn).…”

“…the cervical star, the umbilical cord at the attachment of the amniotic sac, and the mid-part of the pregnant horn). Sequencing revealed a different bacterial composition in the three placental regions ( Hemberg et al . 2023 ), suggesting that the equine placenta might harbor a characteristic microbiome.…”

“…Hemberg et al used culture to detect bacteria in the amniotic fluid of naturally delivered foals in two studies ( Hemberg et al 2015 , Hemberg et al . 2023 ).…”

“…Bacteria did not grow in 75% of cultures from equine amniotic fluid samples. The positive cultures included common contaminants, such as Acinetobacter lwoffii , Streptococcus , Enterococcus faecalis or coagulase-negative staphylococci ( Hemberg et al . 2023 ).…”