Bacterial proteins in semen
Research type
Research Study
Full title
Bacterial proteins in the semen of men and infertility
IRAS ID
168675
Contact name
Patrick Horner
Contact email
Duration of Study in the UK
0 years, 7 months, 1 days
Research summary
Research Summary
Infertility affects 1 in 7 couples, where the cause is unexplained in 25%. It is possible that in some of these cases, bacteria are present in semen and that these bacteria may damage sperm. Many bacteria cannot be detected by current routine tests. Earlier work looking at male sperm as part of this study has found evidence that the detection of a bacterial protein may be associated with the presence of unusual bacteria not normally found in semen but we do not have enough semen samples from fertile and infertile men to be certain that this is associated with infertility. We want to find out whether the presence of this bacterial protein is indeed associated with infertility in men and, if this is the case, which bacteria produce this protein. Obtaining further semen specimens from infertile and fertile men would enable us to establish proof of principle that bacteria in semen is associated with male infertility.
Summary of Results
Sialic acids (a carbohydrate building block) are abundant at the sperm surface where they cap most carbohydrate chains (glycans) which are fixed to the end proteins on the sperm surface. These glycoproteins regulate sperm migration through cervical mucus, are essential for sperm survival and are also necessary for fertilisation of the egg. Bacterial colonization of semen is common, some of which can produce sialidases (enzymes which remove sialic acid from glycan chains) and have the potential to corrupt the glycoproteins on the sperm surface and thus cause subfertility. We used an artificial sialidase substrate to test for sialidase activity in semen from 30 fertile, 59 sub-fertile and 50 men of uncertain fertility status. We undertook semen analysis and used bacterial DNA sequencing to characterize which bacteria were present in the semen from these men. Samples were clustered according to closeness of their bacterial DNA structure and used as input to Principal Component Analysis(PCoA) and a heatmap of the relative abundance of bacterial type constructed. A two class model of sialidase activity best fitted the data (high and low). A sample with raised sialidase activity >1000 absorbance units had a >95% probability that it belonged in the high sialidase class. No association between sialidase activity and abnormal semen parameters was observed. Although no association between raised sialidase activity and infertility was observed, 3/30(10%) fertile, 11/40(27%) uncertain fertility and 8/40(20%) infertile men had raised sialidase activity. Of 16 infertile men with normal sperm, 4(25%) had raised sialidase activity compared to 2(8%) of 25 fertile controls (p=0.186 not significant). Bacterial DNA detection confirmed that semen was not sterile. Neither PCoA nor heatmap analysis demonstrated a difference in bacteria type, between fertile and infertile men and between men with high and low sialidase activity. In conclusion sialidase activity can be detected in human semen. Although no associations between sialidase activity and abnormal semen parameters, infertility or type of bacteria were identifiable, this was a small study. Further studies are merited to establish whether semen colonization with sialidase producing bacteria can cause male subfertility.
REC name
South West - Frenchay Research Ethics Committee
REC reference
15/SW/0093
Date of REC Opinion
2 Apr 2015
REC opinion
Further Information Favourable Opinion