Triclosan alters biofilm structures and confers antibiotic tolerance in Staphylococcus aureus using multiple regulatory pathways

The biocide triclosan is used extensively in both household and hospital settings. The chronic exposure to the biocide occurring in individuals that use triclosan-containing products results in low levels of triclosan present in the human body that has been linked to induction of antibiotic tolerance and altered biofilm formation. Here we aimed to unravel the molecular mechanisms involved in triclosan-induced antibiotic tolerance and biofilm formation in Staphylococcus aureus . Triclosan treatment prior to planktonic exposure to bactericidal antibiotics resulted in 1,000 fold higher viable cell counts compared to non-pretreated cultures. Triclosan pretreatment also protected S. aureus biofilms against otherwise lethal doses of antibiotics as shown by live/dead cell staining and viable cell counting. Triclosan mediated antibiotic tolerance in S. aureus biofilms required an active stringent response because biofilms of a pppGpp ⁰ strain were not protected from antibiotic killing. Incubation of S. aureus with triclosan also altered biofilm structure due to SarA-mediated overproduction of the polysaccharide intercellular adhesin (PIA) in the biofilm matrix. Thus, physiologically relevant concentrations of triclosan can trigger (p)ppGpp dependent antibiotic tolerance as well as SarA dependent biofilm formation.