The Antimicrobial Effects of Hops (Humulus lupulus L.) on Ruminal Hyper Ammonia-Producing Bacteria

Authors: Flythe, Michael

Submitted to: Letters in Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2009
Publication Date: 5/7/2009
Citation: Flythe, M.D. 2009. The Antimicrobial Effects of Hops (Humulus lupulus L.) on Ruminal Hyper Ammonia-Producing Bacteria. The Society for Applied Microbiology, Letters in Applied Microbiology. 48, 712-717.

Interpretive Summary: When ruminants consume feed, as much as half of the amino acid nitrogen can be lost due to microbial degradation in the rumen. Some of the ammonia that is produced is assimilated into microbial protein, which is nutritionally available to the animal. However, much of the ammonia passes into the blood stream, converted into urea and lost. Many rumen microbes can catabolize amino acids, but most of this activity is attributed to a group of bacteria that have been termed hyper ammonia-producing bacteria (HAB). The hops plant (Humulus lupulus L.) is well known for its antimicrobial properties, and these experiments were conducted to determine if hops could be used to control ruminal HAB. Both dried hops flowers and hops extract inhibited ammonia production by mixed rumen microbes that were harvested from a cow. When the pure HAB cultures were incubated with hops extract, growth and ammonia production were inhibited. These results indicate that the antimicrobial components of hops might also reduce ammonia production by ruminal bacteria in vivo.

Technical Abstract: Methods and Results: Media were prepared with dried hops or hops extract (30.7% lupulone), and inhibited ammonia production by mixed rumen bacteria. The growth and ammonia production of pure cultures (Peptostreptococcus anaerobius, Clostridium aminophilum, or Clostridium sticklandii) was inhibited by 30 ppm lupulone at pH 6.7, and bactericidal activity was observed at pH 5.6. When hops extract was added to energized cell suspensions, the intracellular pH rapidly decreased, and intracellular potassium was lost. Conclusions: The three HAB species were sensitive to the antimicrobial components in hops, and the inhibition of ammonia production by mixed rumen bacteria indicates that similar effects could be expected in the rumen. Significance and Impact of the Study: As much as half of the amino acids consumed by ruminants can be lost due to microbial degradation in the rumen. This report supports the idea that biologically active plant metabolites can be used to mitigate this wasteful process.