In-vitro Antimicrobial Effect of Silybum marianum Extract on Bacterial Isolates from the Semen of Infertile Men in Iran

Genital tract infection is one of the main causes of male infertility. The increasing frequency of drug resistance and side effects of antibiotics have urged researchers to seek alternative sources of antimicrobial agents, such as medicinal herbs, for the treatment of antibiotic-resistant infections.

The present study aimed to determine the frequency of potentially pathogenic microorganisms in the semen of infertile men and investigate the antimicrobial activity of Silybum marianum extract against the isolates.

Semen samples were collected from 96 infertile men who referred to the Pasteur Laboratory in Gorgan, Iran. Semen samples were first analyzed according to the World Health Organization guidelines and then underwent microbiological tests to identify pathogens. Antimicrobial susceptibility to S. marianum extract was evaluated using the disk diffusion (Kirby-Bauer) method. Moreover, the active components of the extract were identified by the gas chromatography-mass spectrometry technique.

In the semen analysis, 64% of the samples had problems in the parameters of sperm count, motility, and morphology. In addition, the bacterial contamination was observed in 36% of semen samples. The most and the least common isolates were Staphylococcus aureus (45%) and Klebsiella pneumoniae (11%) and Staphylococcus epidermidis (11%), respectively. In Gram-positive isolates, S. aureus was mostly resistant to azithromycin (57%). In Gram-negative isolates, Escherichia coli was mostly resistant to gentamicin (37%). The inhibitory activity of S. marianum flower extract was significantly higher than that of S. marianum leaf extract (P < 0.01). Silybin (2.64%) and silychristin (3.07%) were the most abundant constituents of S. marianum flower extract.

Bacterial infections play an important role in male infertility and S. marianum extract after purification can be potentially used for the treatment of antibiotic-resistant genital tract infections.