Combination of antimicrobial peptides and isoniazid/rifampicin against multidrug-resistant tuberculosis

Abstract

Multidrug-resistant (MDR) Mycobacterium tuberculosis (Mtb) bearing resistance towards both isoniazid (INH) and rifampicin (RIF) were reported during early 1990s. New anti-TB drug development has been extensively focused, yet the adverse events experienced by patients were substantial. Therefore, innovative approaches to achieve a shortened and safe therapeutic regimen for drug-resistant TB is imperative. The specifi c composition of mycobacterial cell wall giving rise to its extremely high hydrophobicity and impermeability is known to confer Mtb antibiotic resistance. Antimicrobial peptides (AMPs) act selectively on negatively charged bacterial membranes, their pore-forming actions lead to leakage of cellular content and eventually cell death. This killing effect is rapid and potent while making development of resistance to AMPs diffi cult. Our study aims at investigating the combination of novel antimicrobial peptides with fi rst line anti-TB drugs against MDR-TB. D-LAK peptides were shown to exert a detergent-like effect which effectively broke down clumps of bacteria and inhibited the growth of MDR and XDR Mtb strains (1). Therefore, we hypothesize that D-LAK peptides can facilitate the access of anti-TB drugs into mycobacteria by increasing their surface permeability, with the potential of re-sensitizing MDR-TB to fi rst-line anti-TB drugs. Combination treatment of INH and RIF with D-LAK peptides has successfully demonstrated synergistic effect against the growth of MDR-TB strains. Antibacterial assays revealed the effi cacies of bacterial load reduction at a lower anti-TB drug as well as D-LAK peptide concentrations. We have also employed Mycobacterium smegmatis as a model to understand the mechanism of actions of D-LAK peptides. Membrane disruption activity by D-LAK peptides was visualized using transmission electron microscopy (TEM). Prolonged treatment of peptide caused irreversible damage of cell envelope leading to leakage of cellular content. Confocal microscopy has further confi rmed cell surface perturbation action of D-LAK peptides supporting our hypothesis regarding the assistant role of peptides in re-sensitization of MDR-TB towards fi rst-line drugs. Further investigations on the antibacterial mode of action in a whole organism view using nuclear magnetic resonance (NMR) metabolomics is in progress. 1. Lan Y, Lam JT, Siu GK, Yam WC, Mason AJ, Lam JK. Cationic amphipathic D-enantiomeric antimicrobial peptides with in vitro and ex vivo activity against drug-resistant Mycobacterium tuberculosis. Tuberculosis (Edinb). 2014;94(6):678-89.