Antibacterial effects of mixtures of extracts of usnea, thyme and angelica obtained using different technological processes against certain types of bacteria of importance in veterinary medicine

Antibacterial effects of plant extracts were examined using mixtures of extracts obtained using different technological processes: usnea extract was obtained using the process of supercritical extraction (NKE), angelica extract was obtained through supercritical extraction processes (NKE) and ultrasound extraction using ethanol (UZ), and thyme extract was obtained using the process of hydrodistillation (HD). Mixtures of the listed extracts were examined in various ratios: U (NKE) and T (HD) in a ratio of 1:1, U (NKE) and T (HD) in a ratio of 7:3, U (NKE), T (HD) and A (NKE) in a ratio of 2:2:1, and U (NKE), T (HD) and A (UZ) in a ratio of 2:2:1. The investigations covered 15 strains of bacteria of the genus Staphylococcus, Streptococcus and Enterococus, including the strains MRSA, VRE as well as reference strains of S. pyogenes ATCC 19615, S. agalactiae ATCC 27959 and S. aureus ATCC 11632. The antibacterial action of mixes of plant extracts was examined using the microdilution method in bouillon, and the examined mix concentrations were from 1.25 g/mL to 1280 g/mL. The strongest antibacterial effect was exhibited by mixes of usnea (NKE) and thyme (HD) in ratios of 1:1 and 7:3 with obtained MIC values from 5 g/mL to 160 g/mL, but the MIC value of the listed mixtures for the biggest number of strains amounted to 40 g/mL. A somewhat weaker effect was exhibited by the other examined extract mixtures with obtained MIC values of 10 g/mL to 320 g/mL. Based on the obtained MIC values and the results of previous investigations, it can be concluded that the examined mixtures of plant extracts exhibited a very strong antibacterial effect on the examined bacteria strains.