**3. Effect of** *E. coli* **on human spermatozoa is induced through seminal leukocytes**

One way *E. coli* induces damage in spermatozoa is by mediating seminal leukocyte activation. The increased presence of leukocytes in semen, known as leukocytospermia, is defined by a concentration equal to or greater than 1 x 10<sup>6</sup> leukocytes per ml of semen [17]. Proinflammatory cytokines, which are usually released by leukocytes during the inflammatory response, are able to decrease sperm motility by themselves [5, 18, 19]. This damaging effect seems to be mediated by polymorphonuclear (PMN) leukocytes instead of by other leukocytes such as lymphocytes or monocytes [20]. The decrease in sperm quality is also mediated by reactive oxygen species (ROS) released by PMN after bacteria‐induced activation, with *E. coli* being able to induce a higher response of increased ROS production than other bacteria [9]. Other consequences of ROS released by leukocytes are lipid peroxidation, which affects sperm plasma membrane [21, 22], and early induction of sperm capacitation, which should normally occur later in the female reproductive tract [23].
