Pseudomonas aeruginosa adapts to octenidine via a combination of efflux and membrane remodelling

Pseudomonas aeruginosa is an opportunistic pathogen capable of adapting to the antiseptic octenidine by an unknown mechanism. Here, we characterise its adaptation to octenidine in the laboratory, as well as a simulated clinical setting, and identify a novel antiseptic resistance mechanism. In both settings, 2 to 4-fold increase in octenidine tolerance was associated with stable mutations and specific 12bp deletions in a putative Tet-repressor gene (smvR), associated with a constitutive increase in expression of the major facilitator superfamily (MFS) efflux pump SmvA. Adaptation to higher octenidine concentrations led to additional stable mutations, most frequently in phosphatidylserine synthase pssA and occasionally in phosphatidylglycerophosphate synthase pgsA genes, resulting in octenidine tolerance 16 to 256-fold higher than parental strains. This was associated with mitigation of oxidative stress and modification of plasma membrane composition and order. Mutations in both a putative efflux system and lipid synthases therefore enable higher level, synergistic tolerance of octenidine.