Bacterial strains and culture conditions

The salivaricin B producer strain, Streptococcus salivarius K12, was grown on Mitis salivarius agar (MSA) or Columbia agar base supplemented with 5% whole human blood and 0.1% CaCO₃ (BaCa). M17 medium supplemented with 2% yeast extract, 1% sucrose, 0.1% CaCO₃ and 0.7 agarose (M17YESUCa) was used as the salivaricin B production medium.

Indicator strains Micrococcus luteus ATCC10240 and Corynebacterium spp GH17 were grown either on Mueller Hinton agar (MHA) or Trypticase Soy agar (TSA). Streptococcus pyogenes ATCC1234 and Streptococcus mutans GEJ11 were grown either on BaCa plates or TSA. For MIC tests, M17 medium supplemented with 1% glucose (GM17) was used to propagate the streptococcal strains. All streptococci were grown in a microaerophilic atmosphere using GasPak EZ CO2 Container System, BD at 37 °C. M. luteus and Corynebacterium spp were grown aerobically at 37 °C. Lactococcus lactis subsp. cremoris HP was propagated in GM17 at 30 °C. All media were purchased from Difco, BD. Nisin A was purchased from Sigma-Aldrich. All solvents and chemicals were purchased from Merck, Germany. Nisin A stock solution was prepared as described previously⁵⁷.