Bidirectional alterations in antibiotics susceptibility in Staphylococcus aureus - Pseudomonas aeruginosa dual-species biofilm

ABSTRACT While in biofilms bacteria are embedded into an extracellular matrix which forms inaccessible barrier for antimicrobials thereby drastically increasing the concentrations of antibiotics required for treatment. Here we show that the susceptibility of S. aureus and P. aeruginosa to antibiotics in mixed biofilms significantly differs from monoculture biofilms depending on both conditions and chosen antimicrobial agents. While S. aureus could completely avoid vancomycin, ampicillin and ceftriaxone by embedding into the biofilm of P. aeruginosa , the very same consortium was characterized by 10–fold 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. Moreover, similar increase in antibiotics efficacy was observed when P. aeruginosa suspension was added to the mature S. aureus biofilm, compared to S. aureus monoculture, and vice versa. These findings open promising perspectives to increase the antimicrobial treatment efficacy of the wounds infected with nosocomial pathogens by the transplantation of the skin residential microflora.