The influence of neutrophils and their exoproducts on biofilm biomass, bacterial viability and conjugative transfer into Escherichia Coli

The purpose of this study was to investigate the effect of neutrophils and their antimicrobial factors, hydrogen peroxide and defensin α, on the biofilm biomass, the viability of bacteria in the biofilm and the efficiency of conjugative transfer of the pOX38:Cm plasmid from the E. coli N4i pOX38:Cm strain into different E. coli strains (commensal К12 TG1 and uropathogenic DL82, R32 and R45). The biofilm of the recipient E. coli TG1 with the donor E. coli N4i pOX38:Cm increased when 10⁵ cells/ml of neutrophils were added compared to the control, while the biofilm biomass of the uropathogenic E. coli recipient strains DL82/E. coli R45 with the donor E. coli N4i pOX38:Cm decreased when 10⁶/10⁴–10⁶ cells/ml of neutrophils were added, respectively. The survival of recipient E. coli TG1 cells and transconjugants in the biofilm was, compared to the control, higher when 10⁴, 10⁵, 10⁶ cells/ml of neutrophils were added. The addition of 0.1 mM H₂O₂ increased biofilm formation of E. coli DL82 and E. coli R45, and addition of 0.5 mM H₂O₂ reduced biofilm formation of E. coli DL82, while 0.5 mM or 2.5 mM reduced the E. coli R45 bacterial biofilm biomass in the conjugative mixture. The frequency of the pOX38:Cm conjugative transfer was lower in the presence of 2.5 mM H₂O₂ in the N4i pOX38:Cm × DL82 biofilm, and also in the presence of 0.5 and 2.5 mM H₂O₂ in the N4i pOX38:Cm × R45 biofilm, compared to the control. The frequency of pOX38:Cm conjugation from the donor E. coli N4i pOX38:Cm into E. coli DL82 decreased, when 5 or 25 ng/ml defensin α were added and the conjugation frequency in the mating mixture N4i pOX38:Cm×R45 decreased, when 5 ng/ml were added, while, when 25 ng/ml of defensin α were added it increased.