Antibiofilm Platform Based on the Combination of Antimicrobial Polymers and Essential Oils

The development of potent strategies to counter microbial biofilm is an urgent priority in healthcare. The majority of bacterial infections in humans are biofilm related, however, effective treatments are still lacking especially for combating multidrug-resistant (MDR) strains. Herein, we report an effective antibiofilm platform based on the use of synthetic antimicrobial polymers in combination with essential oils, where the antimicrobial polymers play a secondary role as delivery vehicle for essential oils. Two ternary antimicrobial polymers consisting of cationic primary amines, low-fouling oligo(ethylene glycol) and hydrophobic ethylhexyl groups were synthesized in the form of random and block copolymers, and mixed with either carvacrol or eugenol. Coadministration of these compounds improved the efficacy against biofilms compared to the individual compounds. We observed about a 60-75% and 70-85% biofilm inhibition effect for all tested combinations against wild-type PAO1 and MDR strain PA37, respectively, upon 6.5 h of incubation time. While both random and block copolymers demonstrated similar biofilm inhibition potencies in combination with essential oils, only the block copolymer acted synergistically with essential oils in killing biofilm. Treatment of PAO1 biofilm for 20 min with the block copolymer-oil combinations resulted in the killing of >99.99% of biofilm bacteria. This synergistic bactericidal activity is attributed to the targeted delivery of essential oils to the biofilm, driven by the electrostatic interaction between positively charged delivery vehicles, in the form of polymeric micelles, and negatively charged bacteria. This study thus highlights the advantage of combining essential oils and antimicrobial polymers as an effective avenue for antibacterial applications.