Background. Methane emissions from agriculture are responsible for over 40% of the world’s greenhouse gas emissions. In the past, antibiotics were used to control methane production by animals, but concerns over the emergence and spread of antibiotic-resistant bacteria to humans have prompted a search for alternative approaches. Hops are the flowers of the hop plant Humulus lupulus. They have been used to feed cattle for many years and are known to contain antibacterial compounds, and their extracts have been shown to kill members of the Mycobacterium spp including Mycobacterium bovis, the causative agent of bovine tuberculosis as well as a number of human pathogens. In this study, hop extracts were studied for their ability to inhibit methane production from Methanobrevibacter ruminantium, a major methane-producing archaeon found in the rumen of cattle. Methods. Methanobrevibacter ruminantium M1T (DSM 1093) was grown at 37°C for 30 days, and the amount of methane produced at different time points during this period was measured using gas chromatography. The archaeon was exposed to commercial hop extracts (tetra-hydro-iso-alpha acid and beta acid) and to aqueous hop extracts of a range of hop variants, and their effect on methane production was determined. Results. All of the extracts reduced the level of methane production of M. ruminantium over the 30-day period compared to the negative control (sterile distilled water). The commercial hop extracts were the most effective at inhibiting methane production over the course of the experiment in contrast to the aqueous extracts, which showed a gradual reduction of inhibition with time. Conclusions. Hops contain compounds which inhibit methane production. Given that hops can be safely fed to cattle, this raises the possibility of rationally designing a feed strategy which could reduce greenhouse gas emissions and protect against bovine tuberculosis. This study recommends that further research be undertaken to further identifying bioactive components from hops and their efficacy against a range of archaea.

As part of our ongoing research efforts to develop new antibacterial agents acting on novel molecular targets, a series of twenty-two adenine and benzimidazole-based mimics of the lead compound REP-3123 was designed to target methionyl-tRNA synthetase of Clostridium difficile and Bacillus anthracis based on a homology model. Structures of the target compounds were elucidated by means of 1 H and 13 C NMR spectral data and their purity was confirmed by HRMS or microanalyses. The target compounds were tested for their in vitro antibacterial activity against those two challenging organisms by the microdilution method in brain heart infusion broth. Unfortunately, six of the target compounds were not biologically tested due to inadequate solubility in DMSO under the assay conditions. Only the fluoro-substituted adenine-based sulfamide (18) showed activity against C. difficile with an MIC of 85.33 lg/mL. The adenine-based thiourea (32) and diamine (36) were the most promising antibacterial agents against B. anthracis with an MIC of 92.16 lg/mL. The rest of the tested compounds either showed inferior activity (MIC = 102.4 lg/mL) or were totally inactive. Although the compounds were not very active, the biological data are employed as a basis for our currently underway investigation for structure optimization. Ó 2016 Production and hosting by Elsevier B.V. on behalf of Faculty of Pharmacy, Cairo University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

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.