The Antibacterial Effect of Humulus lupulus (Hops) against Mycobacterium bovis BCG: A Promising Alternative in the Fight against Bovine Tuberculosis?

The female flowers of the Humulus lupulus plant or Hops have been used extensively within the brewing industry for their aroma and bitterness properties. It was also found that beer that contained hops was less likely to spoil, thus revealing the antimicrobial potential of these plants. One species of bacteria, Mycobacterium spp., is of particular interest as it is the causative agent of both human and animal forms of tuberculosis (TB). In this study an aqueous extraction process was employed to analyse the antibacterial properties of 50 hop extracts (45 individual variants); against M. bovis BCG. Using an agar well diffusion assay we found that all hops exhibited a level of inhibitory activity which ranged from 1.2 mm (+/− 0.08 mm) in the case of hop variant; Target, to 15.7 mm (+/− 0.45 mm) in the case of hop variant Citra. The Citra variant had a minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 16% v/v. This is the first study to analyse a wide range of hops for their antimicrobial potential against M. bovis BCG and recommends that further research focuses on other Mycobacteria spp., the potential for antimicrobial synergy and the antibacterial effect of individual components.