The mutual alteration of bacterial susceptibility to antimicrobials in dual-species biofilm

Abstract

The biofilm formation by pathogenic bacteria significantly reduces the efficacy of antimicrobial therapy, leads to chronic diseases and slows down the wounds healing. Many infectious processes are caused rather by consortium of bacteria than by one microorganism. As a result, mixed bacterial biofilms are formed, in which the resistance to antimicrobials increases due to the survival of some microorganisms in the biofilm of resistant strains and the transition to an uncultivated state. Here we show that the bacterial susceptibility to antimicrobials in dual-species biofilms significantly differs from monoculture biofilms depending on both conditions and chosen antimicrobial agents. While Staphylococcus aureus could completely avoid some antimicrobials by embedding into the biofilm of various gram-negative bacteria, the very same consortium was characterized by 10fold increase in susceptibility to broad-spectrum antimicrobials like ciprofloxacin and aminoglycosides compared to monocultures. These data clearly indicate that efficient treatment of biofilm-associated mixed infections requires antimicrobials active against both pathogens, since the interbacterial antagonism would enhance the efficacy of treatment.