Interaction of Neutrophils and Biofilm Formed by Uropathogenic Escherichia coli Strains with Different Pathogenic Potential

Abstract

The biofilm formation by uropathogenic E. coli (UPEC) allows bacteria to avoid the influence of the host immune system that determines the pathogenesis of persistent urinary tract infections. The purpose of this work was to evaluate the mutual influence of neutrophils and biofilms formed by UPEC with different set of virulence-associated genes (VAGs). E. coli R11 and R32 strains with a wide range of virulence factors were characterized by low biofilm biomass that did not change after interaction with neutrophils. The biomass index decreased after interaction with neutrophils for strains with a limited set of pathogenicity factors (R33, R36, R45, and R44) and a "thick" biofilm. Bacterial cells and biofilm supernatants of all UPEC strains reduced viability (DiOC₆(3)⁺/PI^-) and stimulated early apoptosis (DiOC₆(3)^-/PI^-) of neutrophils. The number of viable neutrophils was higher, while the number of apoptotic and necrotic (DiOC₆(3)^-/PI⁺) cells was lower under the action of supernatants of strains R44, R36, R45 in comparison with bacterial cells. Thus, modulation of the innate cell functions depends on the realization of the pathogenic potential of UPEC bacteria in urinary tract biofilms that determines the development of recurrent urinary tract infections.

Keywords: biofilms; neutrophils; uropathogenic Escherichia coli (UPEC); virulence-associated genes (VAGs).