Crude alkaloids from Phyllanthus fraternus, Webster: Antibacterial, time-kill kinetics and resistance modulation studies

Abstract

Antimicrobial resistance (AMR) continues to rise, making a growing number of infectious diseases difficult to cure. Millions of people worldwide die from infections with medication resistance. According to the World Health Organization (WHO), a resistant variant has a 64 % higher chance of killing an infected victim than a non-resistant variant. As a result, scientists continue to focus research attention on finding novel chemotypes that could have different modes of action. Combination therapy has the potential to overcome AMR since the therapeutic components work together to suppress the etiological microorganism. In the current study, we investigated the antibacterial properties of crude alkaloidal extract of Phyllanthus fraternus (AEPF) using high-throughput spot culture growth inhibition (HT-SPOTi) assay. We performed time-kill kinetic assays to assess the interactions between the crude alkaloids and test microbial strains. The ability of the crude alkaloids to alter the antimicrobial action of standard tetracycline was evaluated by modulation study. Our findings indicate that P. fraternus alkaloids effectively suppress majority of clinically significant pathogenic strains in vitro. Bactericidal effect was shown by time-kill kinetics against S. aureus, E. coli (ATCC 43888), and E. coli (ATCC 10455). Tetracycline was successfully potentiated against Shigella sp. by the alkaloidal extract. The crude alkaloid extract of P. fraternus included two known alkaloids, epibubbialine and ent-norsecurinine, according to LC-ESI-MS analysis. Taken together, the antibiotic activity of P. fraternus is primarily due to its alkaloids and that the potential exists to develop isolated alkaloids as drug candidates for use in combination therapies against antimicrobial resistance.