Studies related to male reproductive tract microbiota are relatively less as compared to other body sites microbiome studies. Particularly semen and prostrate gland have been shown to have a direct affect on different male reproductive traits and fertility. In a study, it was observed that Firmicutes and Proteobacteria rules bacterial communities in testis, seminal vesicles also contains >50% Firmicutes and semen microbiome is composed of ~50% Firmicutes, ~25% Proteobacteria and ~25% Actinobacteria2. Specifically, semen is colonized by Lactobacillus, Pseudomonas or Prevotella. Lactic acid which is synthesized byLactobacillusbacteria, protects the male reproductive tract from effects of pathogenic gram-negative bacteria. Hence good quality semen is marked based on high abundance of Lactobacillus bacteria. In contrast to vaginal microbiome, seminal microbiome posses less biomass but high variations. In a rodent model, it was observed that seminal microbiome plays vital role in successful implantation of embryo and in development of placenta8.
Male reproductive tract microbial dysbiosis:
Microbes particularly bacteria could affect sperm quality and in turn could influence male fertility e.g. different studies provides association of Chlamydia trachomatis with male infertility. Direct evidence of free radical theory of male infertility includes attachment of Escherichia coli to sperm cells which leads to loss of sperm mobility and clumping of sperm cells.The morphology of sperm gets disrupted and the secretions of bacterial membrane proteins e.g. porins etc., effects sperm functions either via production of reactive oxidative species (ROS) or by hampering macrophages from performing their function. In case of humans, idea about microbial particularly bacterial part in causation of male sterility is still considered vague. But some studies do provides evidence that reproductive success of ejaculate gets affected enough by bacterial infections3. Continuous series of events are involved in ejaculation where the ultimate goal is activation of sperm so that it fertilizes egg.Prostate gland plays a major part in this cascade by secreting prostrate fluid that contains Zn ions, citrate and kallikreins. If prostate gland function gets disrupted e.g. in prostatitis, it could lead to male infertility.Bacterial infections e.g.Escherichia coli, disrupts secretory process of prostate gland and thus in turn alters sperm cells parameters11. In normal/healthy individuals, prostatic fluid contains abundant amounts of antimicrobial substances e.g. lactoferrins, defensins. Also, integrity of luminal epithelium is maintained in healthy individuals and is colonized by such microbes that do not initiate inflammatory response. In case of disease condition e.g. prostatic atrophy, which is characterized by reduction in cytoplasmic volume of acinic epithelium(Atrophy, n.d.),certain changes in terms of antimicrobial compounds found in prostatic secretion occurs. This leads to excessive growth of urinary microbiota in luminal region of prostrate ducts, resulting in destruction of epithelial barriers and microbial invasion into and between epithelial cells causing inflammation. Exactly whether microbial imbalance is involved in causation or is the outcome of disease state is not well understood. Microbial imbalance is also involved in occurrence of prostrate cancer1.Table below highlights impact ofmicrobes on different organisms reproductive features.
|Non-human Host Organism||Affects||Reference|
|Staphylococcus aureus lessens sperm movement, viability, structure, and level of ATPase.||3|
|E. colipresence in semen was positively correlated with sperm clumping and negatively associated with litter size.||3|
|Incubation with Campylobacter fetus strainsresulted in drop of sperm motility and viability, and enhanced formation of abnormal shaped sperms.||3|
Gallus gallus domesticus
|In vitro studies involving incubation with six different bacteria i.e Salmonella enterica, E. coli, Campylobacter jejuni, Clostridium bifermentans, Lactobacillus acidophilus, and Bifidobacterium animalis reduced sperm mobility trait expressively.||3|
|Similar to chicken, in vitro study using six different bacteria i.e.
S. enterica, E. coli, C. jejuni, C. bifermentans, L. acidophilus, and B. animalisresulted in reduced sperm movements.
|Cricket iridovirus (CrIV) /Insect iridovirus type 6, IIV-6 resulted in complete or partial drop in sperm mobility trait.||3|
|Exposure to polymicrobial mixture containing Acinetobacter,
Alcaligenes, Bacillus, Staphylococcus, and Streptococcus enhanced sperm mobility at the rate of 40%.