**5. Soluble products of** *E. coli* **also affect human sperm function**

The effects of *E. coli* soluble products on sperm have been studied using supernatants of *E. coli* culture as a source of bacterial metabolic product. It has been reported that although the direct contact with *E. coli* was able to alter sperm motility, the metabolic products of *E. coli* had no effect on decreasing motility in human spermatozoa [24]. However, after this report, it was shown that incubation with the soluble factors of *E. coli* reduced sperm motility and ΔΨm [33]. Added to this, the ability of *E. coli* soluble factors to decrease motility, viability, ΔΨm and increase ROS in spermatozoa can be prevented by lactobacilli. In an *in vitro* experiment, after adding lactobacilli to simulate the normal condition in the female genital tract, the harmful effects of *E. coli* soluble factors were inhibited [44].

Among the soluble factors of *E. coli,* a component called spermatozoa immobilization factor (SIF) was first described in 1977. The effect of SIF, as the name implies, is to immobilize spermatozoa, and this effect could be reversed by washing the spermatozoa [45]. Years later, an apparently similar SIF of 56 kDa was isolated and purified from supernatants of a strain of *E. coli.* SIF‐56 decreases sperm motility completely and almost instantaneously. It was also observed that SIF‐56 at very high concentrations can even induce sperm death [46]. Sperm immobilization mediated by SIF‐56 has been shown to depend on 115 kDa‐receptor present in sperm [47]. Another *E. coli*

soluble factor described is the sperm agglutinating factor (SAF) of 71 kDa, which produces sperm agglutination, decreases ATPase activity and can cause sperm death [48]. A toxin candidate to be further investigated is HlyA, because this toxin is produced by *E. coli* strains most pathogenic to sperm both *in vitro* and *in vivo* [42].
