Preterm prelabour rupture of the fetal membranes (PPROM) is a significant contributor to the morbidity and mortality of prematurity, largely due intrauterine infection, or chorioamnionitis. The placental microbiome present with PPROM has not been specifically reported.
We performed a prospective study of women with PPROM at risk of developing chorioamnionitis. Placenta and blood were collected (on the day of delivery) from women with PPROM. Sub-groups were i) PPROM and confirmed (histological) chorioamnionitis (placenta: n=2, blood: n=4), ii) PPROM without histological chorioamnionitis (placenta: n=2, blood: n=2) and iii) women who delivered preterm without ruptured membranes (placenta: n=2). A placenta from a normal term pregnancy was also included (placenta: n=1). Genomic DNA was extracted from both blood samples (PAXgene tubes) and placenta. 16S rRNA sample transcripts were sequenced using next-generation (Roche 454 GS-FLX) pyrosequencing (NGS) to determine the microbiome.
Unsupervised hierarchical cluster analysis revealed distinct clusters for the peripheral blood microbiome compared to the placenta of women with PPROM, both with and without chorioamnionitis. Analysis of microbiome profiles revealed increased microbial diversity within placenta compared to the blood microbiome. Diversity in the placenta was greatest in the samples from women with PPROM and histological chorioamnionitis (Shannon diversity index [SDI] 5.1), and least diverse in the healthy term sample (SDI 4.6). Evaluation of the taxonomic composition of these samples revealed Archaea was abundant in placental tissue and Firmicutes more abundant in blood microbiota.
This study is among the first reported to describe the placental microbiome using NGS. Overall, NGS has detected a much larger microbial population than that conventionally reported from culture-based methods of identifying bacteria. Those women with PPROM and who develop chorioamnionitis have a greater diversity of microbiota compared to those who do not become infected. Use of NGS approaches may further illuminate the aetiology of chorioamnionitis.