The role of Escherichia coli isolates from the semen in the etiology of male infertility, was investigated in this study. Several possible virulence factors of E. coli, such as possession of 0 antigens or certain K antigens (K,, K5), the type of fimbriae, resistance to antimicrobial drugs and adherence studies to various mammalian sperm cells were examined. It was found that out of 181 E. coli isolates 76.4% belonged to four different urinary serotypes: 0,, 0,, 0, and 0, (5.7y0, 7.5y0, 17.0% and 46.2y0, respectively). The predominant fimbrial phenotype (81.2%) was T l F + / P -, while 15.8% showed also the possession of P fimbriae ( T l F + / P + ) . No isolate was found with the T l F -/ P+ phenotype. The possession of antigens K,, K, was found to be low (12% only). A relatively high level of adherence to different mammalian sperm cells was found among E. coli isolates. 43% of the E. coli isolates were resistant to doxycycline (the drug of choice) and additionally, most of these were resistant also to ampicillin. We suggest that there is a close subpopulation of E. coli which possess certain virulence properties and have the potential to adhere to sperm cells and to colonize on other target tissues in the male genital tract. Such virulent strains may cause asymptomatic male infertility and may be termed male genital tract (MGT)-E. coli.

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