The presence of pathogenic bacteria in semen is a main criterion for male accessory gland infection (Rowe et al., 2000) and one of the leading causes for infertility in men (Pellati et al., 2008).

Indeed, a series of in vitro studies demonstrated the noxious effect of various seminal pathogenic bacteria on sperm quality. For example, the interaction of adhesions like type 1 fimbriae and P-fimbriae present in uropathogenic Escherichia coli (E. coli) with spermatozoa resulted in sperm agglutination and motility reduction (Monga and Roberts, 1994, Wolff et al., 1993). The harmful effect of E. coli, gram-positive Staphylococcus haemolyticus and anaerobic Bacteroides ureolyticus on the integrity of sperm membrane was reported by Fraczek et al. (2012). Ureaplasma urealyticum (U. urealyticum) another uropathogenic microorganism was associated with attenuated sperm motility and alterations in sperm membrane penetrability (Núñez-Calonge et al., 1998). Furthermore, Chlamydia trachomatis (C. trachomatis) compromised the fertilizing capacity of spermatozoa through induction of apoptosis (Satta et al., 2006).

These experimental studies, however, could not be corroborated thoroughly by some findings. The comparison of semen characteristics of two infertile groups with and without pathogens revealed no significant differences (Comhaire et al., 1980). Similarly, Filipiak et al. (2015) and Ombelet et al. (1997) found no association between seminal aerobic pathogens and standard semen parameters. Furthermore, some studies on the effects of specific bacterial strains on sperm quality revealed no significant findings. For instance, the presence of U. urealyticum as well as C. trachomatis was not correlated with abnormal semen parameters (Gregoriou et al., 1989). This result was confirmed by two separate study groups (Andrade-Rocha, 2003, Vigil et al., 2002). Likewise, Vilvanathan et al. (2016) could not establish an association of seminal gram-positive cocci and gram-negative bacilli with sperm abnormalities.

Based on the available literature, the impact of asymptomatic presence of urogenital pathogens on sperm quality remains unknown. Moreover, whether the presence of pathogens within the urogenital tract of asymptomatic males can be associated with an inflammatory process is still not clear. If there would be an established association, antibiotic treatment may be an appropriate therapeutic approach for these men. Hence, we conducted this study on asymptomatic subfertile males to evaluate the effect of potential pathogenic bacterial strains on standard semen parameters, sperm kinematics, and inflammatory markers such as seminal leukocytes and Interleukin (IL)-6.