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 of Streptococcus suis was determined by the disk diffusion test. The broth microdilution method was used to determine the minimal inhibitory and minimal bactericidal concentration (MIC and MBC) of the four selected oils. Furthermore, the bactericidal power (ratio MBC/MIC) was calculated. The EOs 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 the EOs showed notable antimicrobial activity (MIC 90 and MBC 90 312.5–625 μg·ml−1) and a strong bactericidal power (ratio = 1). This is the first study that selects essential oils against S. suis. New studies about the possible synergic effect of EOs with antibiotics and about toxicity and efficacy in in vivo conditions are recommended.
Highlights
Streptococcus suis is a major gram-positive swine pathogen associated with a wide variety of pig diseases, such as meningitis, arthritis, bronchopneumonia, endocarditis, polyserositis, and septicemia
The essential oils with the major antimicrobial activity in the paper disk diffusion assay were selected to determine the minimal inhibitory concentration (MIC) and the minimal bactericidal concentration (MBC), using the broth dilution method for bacteria isolated from animals (CLSI VET01-A4, 2013)
The repeated-measures ANOVA test was used for the selection of the four essential oils with the highest antimicrobial potential in the disk diffusion assay, whereas differences between Essential oils (EOs) were estimated by comparison of main effects
Summary
Streptococcus suis is a major gram-positive swine pathogen associated with a wide variety of pig diseases, such as meningitis, arthritis, bronchopneumonia, endocarditis, polyserositis, and septicemia. KEYWORDS antimicrobial activity, essential oils, MIC, Streptococcus suis, vapor The essential oils with the major antimicrobial activity in the paper disk diffusion assay were selected to determine the minimal inhibitory concentration (MIC) and the minimal bactericidal concentration (MBC), using the broth dilution method for bacteria isolated from animals (CLSI VET01-A4, 2013).
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