Effective killing of Mycobacterium abscessus biofilm by nanoemulsion delivery of plant phytochemicals.

UNLABELLED: Mycobacterium is an acid-fast, aerobic, non-motile, and biofilm-forming bacterium. The increasing prevalence of mycobacterial infections makes it necessary to find new methods to combat the resistance of bacteria to conventional antibiotics. Mycobacterium abscessus is an emerging pathogen that is intrinsically drug resistant due to several factors, including an impermeable cell envelope, drug efflux pumps, target-modifying enzymes, and the ability to form thick, robust biofilms. Phytochemicals are promising antimicrobials; however, their poor solubility in water and their inability to penetrate biofilms render them inefficient in killing bacterial biofilms. In this study, we demonstrate the efficacy of polymer-stabilized phytochemical nanoemulsions in killing M. abscessus biofilms. These nanoemulsions improve the solubility and stability of the phytochemicals and enable biofilm penetration and eradication. We show that the phytochemical emulsions effectively eliminated M. abscessus in an in vitro biofilm model and killed non-replicating persister cells in the Wayne hypoxia model. These nanoemulsions were also effective in vivo in a wound infection model. These findings demonstrate the potential of polymer-stabilized phytochemical nanoemulsions as a promising alternative to conventional antibiotics for the treatment of mycobacterial infections.

IMPORTANCE: Mycobacterium abscessus is among the opportunistic bacterial pathogens that cause nontuberculous mycobacterial diseases. The infection caused by M. abscessus is difficult to treat because the bacterium is resistant to many of the currently available antibiotics, limiting chemotherapeutic strategies. Furthermore, it forms biofilms in clinically relevant settings, making the infection difficult to treat. Many phytochemicals have potent antimicrobial activities, but their hydrophobicity limits clinical applications. In this study, we tested a new drug delivery strategy where hydrophobic plant phytochemicals were emulsified with a biodegradable nanosponge. We show that the emulsification makes phytochemicals such as carvacrol and eugenol more effective against M. abscessus biofilms. We further demonstrate that nanoemulsified phytochemicals can kill hypoxia-induced dormant M. abscessus and effectively improve skin wound infection in mice. Our data pave the way to use phytochemical nanosponge as a platform to create synergy by combining other antimycobacterial drugs.