Essential oils (EOs) have been gaining popularity in the past decades among researchers due to their potential to replace conventional chemicals used in the fight against pests, pathogenic and spoilage microbes, and oxidation processes. EOs are complex mixtures with many chemical components, the content of which depends on many factors-not just the plant genus, species, or subspecies, but also chemotype, locality, climatic conditions, phase of vegetation, method of extraction, and others. Due to this fact, there is still much to study, with antimicrobial effect being one of the key properties of EOs. There are many methods that have been frequently used by researchers for in vitro evaluation; however, although the research has been going on for decades, an internationally accepted standard is still missing. Most of methods are based on time-proven standards used for the testing of antibiotics. Due to the specific properties of EOs and their components, such as volatility and hydrophobicity, many modifications of these standard procedures have been adopted. The aim of this review is to describe the most common methods and their modifications for the testing of antimicrobial properties of EOs and to point out the most controversial variables which can potentially affect results of the assays.

• Keywords
• agar diffusion, agar dilution, antibacterial, biofilm, broth dilution, plant extracts, vapor phase,
• Publication type
• Journal Article MeSH
• Review MeSH

INTRODUCTION: Candida albicans is a significant human pathogen with the ability to form biofilms, a critical factor in its resistance to antifungal treatments. This study aims to evaluate the antifungal activity and biofilm inhibition potential of Tea Tree Oil (TTO) derived from Melaleuca alternifolia cultivated in Vietnam. METHODS: The antifungal activity of TTO was assessed by determining the Minimum Inhibitory Concentration (MIC), Minimum Fungicidal Concentration (MFC), Minimum Biofilm Inhibitory Concentration (MBIC), and Minimum Biofilm Eradication Concentration (MBEC) using broth dilution methods. The experiments were conducted on C. albicans in both planktonic and biofilm states across concentrations ranging from 0.1 μL/mL to 10 μL/mL. RESULTS: TTO demonstrated significant antifungal efficacy, with a MIC of 0.1 μL/mL (∼91.217 μg/mL) and an MFC of 10 μL/mL (∼9121.7 μg/mL). It effectively inhibited biofilm formation with a recorded MBIC of 2 μL/mL (∼1824.34 μg/mL). However, MBEC values were not determinable as the concentrations tested did not achieve the eradication of more than 50% of mature biofilm within the experimental conditions. DISCUSSION: These findings highlight TTO as a promising natural antifungal agent with strong biofilm-inhibitory properties. However, its limited efficacy in eradicating mature biofilms underscores the need for further studies, potentially involving higher concentrations or synergistic combinations with conventional antifungal agents.

• Keywords
• Candida albicans, Minimum Biofilm Inhibitory Concentration (MBIC), Minimum Fungicidal Concentration (MFC), antifungal, biofilm, biofilm inhibition, modified tea tree oil formulation, tea tree oil,
• Publication type
• Journal Article MeSH

Yersiniosis is an important zoonotic disease; however, data are scarce on the resistance of enteropathogenic yersiniae, especially that of Y. pseudotuberculosis. Minimum inhibitory concentrations (MIC) of 21 antibiotics and 3 essential oils (EOs) were determined by broth microdilution for Y. enterocolitica bioserotype 4/O:3 strains isolated from domestic swine (n = 132) and Y. pseudotuberculosis strains isolated from wild boars (n = 46). For 15 of 21 antibiotics, statistically significant differences were found between MIC values of Y. enterocolitica and Y. pseudotuberculosis. While Y. enterocolitica was more resistant to amoxiclav, ampicillin, cefotaxime, cefuroxime, gentamicin, imipenem, meropenem, tetracycline, tobramycin, and trimethoprim, Y. pseudotuberculosis was more resistant to cefepime, ceftazidime, colistin, erythromycin, and nitrofurantoin. Statistically significant differences were found between various essential oils (p < 0.001) and species (p < 0.001). The lowest MICs for multiresistant Y. enterocolitica (n = 12) and Y. pseudotuberculosis (n = 12) were obtained for cinnamon (median 414 and 207 μg/mL, respectively) and oregano EOs (median 379 and 284 μg/mL), whereas thyme EO showed significantly higher MIC values (median 738 and 553 μg/mL; p < 0.001). There was no difference between Y. enterocolitica strains of plant (1A) and animal (4/O:3) origin (p = 0.855). The results show that Y. enterocolitica is generally more resistant to antimicrobials than Y. pseudotuberculosis.

• Keywords
• antibiotic resistance, antimicrobials, broth microdilution, minimum inhibitory concentration, multiresistance, susceptibility,
• Publication type
• Journal Article MeSH