2.8. Determination of Antibacterial Activity

The inhibitory effect of different concentrations (125–2000 μg·mL⁻¹) of lyophilized infusion and pure compounds (gallic acid, catechin and quercetin) on the growth of L. monocytogenes EGD (serotype 1/2a), L. monocytogenes Scott A (serotype 4b), L. monocytogenes NCTC 4885 (serotype 4b), L. monocytogenes NCTC 4994 (serotype 4b), L. monocytogenes ATCC 23074 (serotype 4b), L. monocytogenes NCTC 1792 (serotype 4b), L. monocytogenes NCTC 7973 (serotype 1/2a), Staphylococcus aureus ATCC 6538, Salmonella enterica subsp. enterica serovarm, Enteritidis NCTC 5188 and Escherichia coli ATCC 11775 was determined by the broth microdilution method [23]. An aliquot of overnight bacterial cultures (10 μL) was enriched with 90 μL of fresh broth and subsequently mixed with 100 μL of tested infusion or pure compounds. Microbial growth kinetic was recorded on a Multiskan^™ GO Microplate Photometer (Thermo Fisher Scientific, Vantaa, Finland). Optical density was read at 600 nm by taking measurements every 30 min for 18 h in controlled conditions of 37 °C. An agitation for 10 s was performed to achieve homogeneous suspensions before each measurement. All experiments were performed in triplicate. The minimum inhibitory concentration (MIC) was defined as the lowest concentration of infusion or pure compound at which bacterial growth was inhibited compared to the control.