Antimicrobial activity of selected essential oils againstStreptococcus suisisolated from pigs

Abstract The inhibitory potential by contact and vapor of basil, cinnamon, clove, peppermint, oregano, rosemary, common thyme, and red thyme essential oils (EOs) against 20 strains ofStreptococcus suiswas determined by the disk diffusion test. The broth microdilution method was used to determine the minimal inhibitory and minimal bactericidal concentration (MICandMBC) of the four selected oils. Furthermore, the bactericidal power (ratioMBC/MIC) was calculated. TheEOs with the major potential in the disk diffusion method were red thyme, common thyme, oregano, and cinnamon (∅ mean 16.5–34.2 mm), whereas cinnamon did not show vapor activity. In the microdilution test, all theEOs showed notable antimicrobial activity (MIC90andMBC90312.5–625 μg·ml−1) and a strong bactericidal power (ratio = 1). This is the first study that selects essential oils againstS. suis. New studies about the possible synergic effect ofEOs with antibiotics and about toxicity and efficacy in in vivo conditions are recommended.