The susceptibility of Proteus mirabilis and Enterococcus faecalis to various antimicrobial agents in polymicrobial biofilms formed using a drip flow reactor

Abstract

Objectives: Interspecies interactions in poly-species biofilm are substantial. Our aim is to set up dynamic biofilm models of Enterococcus faecalis and Proteus mirabilis using Drip Flow Biofilm Reactor (DFR) and to evaluate the effect of these dual population on anti-biofilms of some antimicrobials. Materials and Methods: E.faecalis and P.mirabilis biofilms were formed in a DFR. Influences of the dual interactions on their susceptibilities to antimicrobial agents (disinfectants, antibiotics and probiotic strains) were determined. Results: Gluteraldehyde and quaternary ammonium compounds (QAC) effectively killed the cells in both biofilms of E.faecalis and P.mirabilis. However, the efficacy of hydrogen peroxide (H2 O2 ) was dependant on the microbial species present. P. mirabilis was less susceptible to the ampicillin and ciprofloxacin in co-culture compared to when cultured alone. Here, the influence of the presence of E.faecalis on P.mirabilis susceptibility was determined. For high concentrations of ciprofloxacin (1024 and 512 μg/ml), the log reduction in P.mirabilis cells was determined as approximately 4.5 and 3.5 in mono and dual-species biofilms respectively. Compared to B.lactis, L.acidophilus was found to be more effective both on single and dual species. Conclusion: The effect of antimicrobial agents on microbial cells in a polymicrobial biofilm may depend on the composition of the biofilm.