Pseudomonas aeruginosaincreases the sensitivity of biofilm-grownStaphylococcus aureusto membrane-targeting antiseptics and antibiotics

Abstract

AbstractPseudomonas aeruginosaandStaphylococcus aureusoften cause chronic, recalcitrant infections in large part due to their ability to form biofilms. The biofilm mode of growth enables these organisms to withstand antibacterial insults that would effectively eliminate their planktonic counterparts. We found thatP. aeruginosasupernatant increased the sensitivity ofS. aureusbiofilms to multiple antimicrobial compounds, including fluoroquinolones and membrane-targeting antibacterial agents, including the antiseptic chloroxylenol. Treatment ofS. aureuswith the antiseptic chloroxylenol alone did not decrease biofilm cell viability; however, the combination of chloroxylenol andP. aeruginosasupernatant led to a 4-log reduction inS. aureusbiofilm viability compared to exposure to chloroxylenol alone. We found that theP. aeruginosa-produced small molecule 2-n-heptyl-4-hydroxyquinoline N-oxide (HQNO) is responsible for the observed heightened sensitivity ofS. aureusto chloroxylenol. Similarly, HQNO increased the susceptibility ofS. aureusbiofilms to other compounds, including both traditional and non-traditional antibiotics, which permeabilize bacterial membranes. Genetic and phenotypic studies support a model whereby HQNO causes an increase inS. aureusmembrane fluidity, thereby improving the efficacy of membrane-targeting antiseptics and antibiotics. Importantly, our data show thatP. aeruginosaexoproducts can enhance the ability of various antimicrobial agents to kill biofilm populations ofS. aureusthat are typically difficult to eradicate, providing a path for the discovery of new biofilm-targeting antimicrobial strategies.ImportanceThe thick mucus in the airways of cystic fibrosis (CF) patients predisposes them to frequent, polymicrobial respiratory infections.Pseudomonas aeruginosaandStaphylococcus aureusare frequently co-isolated from the airways of individuals with CF, as well as from diabetic foot ulcers and other wounds. Both organisms form biofilms, which are notoriously difficult to eradicate and promote chronic infection. In this study, we have shownP. aeruginosasecreted factors can increase the efficacy of compounds that alone have little or no bactericidal activity againstS. aureusbiofilms. In particular, we discovered thatP. aeruginosaexoproducts can potentiate the anti-staphylococcal activity of phenol-based antiseptics and other membrane-active drugs, including non-traditional antibiotics. Our findings illustrate that polymicrobial interactions can dramatically increase antibacterial efficacyin vitro, and may guide new approaches to target persistent infections, such as those commonly found in respiratory tract infections and in chronic wounds.