Researchers from the Wayne State University School of Medicine, Michigan, the CReATe Fertility Centre, Toronto, Canada, and the University of Massachusetts Amherst, Massachusetts, looked in-depth at the microbiome of human sperm using RNA sequencing. The researchers found that the sensitivity of the method can offer reliable identification of non-human RNA and can indicate both the contaminant species and the extent of the bacterial colonisation.
The researchers isolated sperm and extracted RNA from 85 semen samples. The RNA was sequenced and any human genetic material excluded, then they matched the non-human RNA to genes from a variety of microbial species. These data gave a picture of the 'microbiome' of each sample.
Dr Stephen Krawetz of Wayne State University School of Medicine, Michigan said, 'we show that non-targeted sequencing of human sperm RNA has the potential to provide a profile of micro-organisms (bacteria, viruses, archaea); this information was recovered from the data typically cast aside as part of routine nucleic acid sequencing; the enhanced sensitivity and specificity of the sequencing technology as compared to current approaches may prove useful as a diagnostic tool for microbial status as part of the routine assessment as we move toward personalised care'.
All of the samples showed comparable levels of bacteria and covered species that are normally expected to be found in the male reproductive tract. However, one sample had unusually high levels of microbial sequences from the genus of Streptococcus agalactiae. These bacteria are a leading cause of neonatal infection and can cause issues during pregnancy and post-delivery. They are also linked to significant mortality in premature births, and can cause life-threatening infections in people with compromised immunity.
'Given the recent increase and severity of Streptococcus (agalactiae) infection, as well as others in adults, neonates and newborns, non-targeted human sperm RNA sequencing data may, in addition to providing fertility status, prove useful as a diagnostic for microbial status,' Dr Krawetz said.
The current method most commonly used for investigating male reproductive tract microbes is culturing the samples, but this method can be limiting as not all pathogens can be cultured. With RNA sequencing costs falling, this method may come into wider use and thus gives the opportunity to investigate the human biome completely.