Inhibition of Various Hops Extracts on Streptococcus Mutans Biofilm Formation

Indianapolis, IN

Streptococcus mutans, a commonly studied bacterium, is known to be correlated with human dental caries. This association is seen as the organism forms an oral biofilm on the tooth to promote colonization. S. mutans metabolizes sucrose in the oral cavity to form acids, causing dental caries and tooth decay. Smokers have increased caries and oral biofilms and nicotine enhances in vitro S. mutans biofilm formation. On the other hand, the female flower of the plant called Humulus lupulus, known collectively as hops, was many years ago added to certain products for its supposed antimicrobial effects. Although there is controversial evidence, the most widely known example of this is beer, as the dried flower was added to preserve the beverage during the long voyage from England to India. The purpose of this study was to compare hops which varied in their beta acid concentrations and how this affected S. mutans biofilm formation. S. mutans biofilm was created in the laboratory in order to mimic biofilm in the oral cavity. Cultures of S. mutans UA159 were grown overnight in tryptic soy broth (TSB) then diluted 1:200 in various nicotine concentrations in TSB containing 1% sucrose ranging from 0.25-32 mg/ml for 24 hours at 37°C in 5% CO2 in 96-well microtiter plates and the amount of biofilm growth measured. This served as a control and simulated nicotine exposure in smokers. Ten different hops extracts (initial concentration of 6.6 mg dried hops/ml of distilled water) with beta acid concentrations ranging from 2.6 to 8.1% were boiled for 90 minutes, then filter sterilized, and diluted from 1:2-1:256 to imitate the levels commonly found in beer. S. mutans was added to each diluted hop extract in a 96-well microtiter plate similar to the nicotine control and the biofilm measured. This process was repeated three times. All hops significantly inhibited (p < 0.05) the overall growth and biofilm formation in each trial. The exposure of nicotine to S. mutans enhanced the overall growth and biofilm formation of S. mutans; however, when the bacterium was added to the various hops extracts, strong biofilm inhibition was observed suggesting that a component of hops is inhibitory to S. mutans. These results imply that hops contain a substance that may lead to a possible decrease in the risk of caries.