Background and Objective: Chlamydia trachomatis infection is one of the most common sexually transmitted diseases especially in western countries. While there is agreement on the manifestations and, in particular, the negative effects of Chlamydia infection on female fertility, the role of this organism in male fertility is still controversial. In addition to Chlamydia, some bacteria belong to the enterobacteriaceae family, including E.coli, Klebsiella, and Serattia have been suggested in human sperm dysfunction. The purpose of the present study was to compare the in vitro toxic effects of lipopolysaccharides (LPSs) extracted from these bacteria on human sperm. Materials and Methods: In this labratory study, 5 × 106 sperm/ml of prepared sperm using percoll gradient method were treated with 0.1, 1, 10, 25, and 50µg/ml of commercial LPSs from E.coli, Klebsiella, and Serattia and 0.1µg/ml of lab-made Chlamydia LPS at 37ºC in 5% CO2 for 6 hours. After 6h incubation the sperm viability was measured using the HOS test. Results: Commercial LPSs used in this study had no significant detrimental effects on human sperm at lower than 50µg/ml while Chlamydia LPS at 0.1µg/ml showed a significant toxic effects against sperm compare to control group (38.6±1%, p<0.05). Conclusion: Although, chlamydia infections are almost clinically chronic and asymptomatic, our findings showed that the in vitro spermicidal activity of this bacterium is about 500 times more potent than the LPS of E.coli, Klebsiella, and Serattia. These results and the findings from the other relevant studies confirm the key role of C.trachomatis as one of the infectious factors causing male infertility. Key words: Lipopolysaccharides, Chlamydia, Enterobacteriaceae, Sperm, Male Infertility Funding: This research was funded by Rafsanjan University of Medical Science and conducted at the University of Sheffiled. Conflict of interest: None declared. Ethical approval: The Ethics Committee of Rafsanjan University of Medical Sciences and Sheffiled University jointly approved the study.

Keywords: Lipopolysaccharides, Chlamydia, Enterobacteriaceae, Sperm, Male Infertility

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