Production of soluble virulence factor by Escherichia coli

Experimental evidence suggests that adherence is a prerequisite for bacterial infection. We demonstrated that transitional cells at the surface of the bladder are coated with glycosaminoglycans (proteoglycans and mucus) whose presence efficiently decreases bacterial adherence to the mucosa. Exposure of mucus to protamine sulfate, a quaternary amine (known to form salts with glycosaminoglycans and inactivate them) significantly increases the bacterial adherence to the bladder. Investigators have primarily focused on bacterial surface factors (that is pili or fimbriae, glycocalix) in relation to the ability to adhere. We explored the hypothesis that Escherichia coli produces a soluble virulence factor that increases the infection rate in rabbits by promoting bacterial adherence to the bladder mucosa. In addition, it was proposed that this factor is a quaternary amine similar to protamine. For these studies an in vivo bacterial infection assay (which we described previously in rabbits) was used to examine E. coli metabolic products (soluble virulence factor) that could promote bacterial persistence in the bladder by perturbing mucus (glycosaminoglycans), and promote bacterial adherence and virulence. E. coli was grown in human urine and a bacterial-free supernatant was collected. Rabbit bladders were then exposed to either this supernatant or to the same human urine that was not infected with E. coli. Results show a significantly higher bacterial persistence (bacterial count) in bladders pretreated with urine containing the E. coli supernatants compared to controls pretreated with uninfected urine (p = 0.03). The molecular weight of the putative soluble virulence factor is less than 3.5 kD. (p = 0.056) based on dialysis studies and binds to heparin agarose affinity chromatography matrix, suggesting that it is cationic and capable of adhering to the highly anionic bladder mucus (glycosaminoglycans).