Extracellular DNA enhances Pseudomonas aeruginosa biofilm resistance to sodium hypochlorite stress.

The opportunistic human pathogen Pseudomonas aeruginosa exhibits high pathogenicity and antimicrobial resistance, largely due to its ability to form robust biofilms. In addition to the exopolysaccharides Psl and Pel, extracellular DNA (eDNA) is an important matrix component in P. aeruginosa PAO1 biofilms. It has been shown previously that eDNA is involved in biofilm initiation and integrity as well as antibiotic resistance, however, it's involvement in resistance to oxidative stressors such as the widely used disinfectant sodium hypochlorite (NaOCl) is less explored. Here, we examined the function of eDNA in NaOCl resistance of P. aeruginosa PAO1 biofilms. Using different biofilm assays in combination with a PAO1 ∆pslA pelF double mutant, which lacks the exopolysaccharides Psl and Pel, and a Tn-bfmR mutant, which exhibits increased eDNA amounts in biofilms, we were able to show that eDNA contributes to NaOCl resistance in P. aeruginosa PAO1 biofilms, in particular when exopolysaccharides are absent. Interestingly, NaOCl was more effective after DNAse treatment against ∆pslA pelF biofilms. These findings indicate that the protective function of eDNA in biofilm resistance is matrix composition-dependent and becomes more pronounced in the absence of Psl and Pel.