## 2 Materials and Methods
### Streptococcus mutans and Candida albicans Strains and Growth Conditions  
The _S. mutans_ strain was isolated identified and characterized by standard laboratory methods (kindly provided by Professor [PERSON], School of Dentistry, Aristotle University, Thessaloniki, Greece). _S. mutans_ was routinely grown in Brain Heart Infusion (BHI) broth or agar (Conda, Madrid, Spain) according to CISI (former NCCLS) guidelines. _C. albicans_ was identified and characterized by standard laboratory methods (kindly provided by Professor [PERSON], School of Medicine, Aristotle University, Thessaloniki, Greece). _C. albicans_ was routinely grown in RPMI 1640 supplemented with w/25 mM Hepes w/L-Glutamine (Biosera, Cholet, France) or Sabouraud dextrose agar (Neogen, Heywood, UK) according to the CISI (former NCCLS) guidelines. Determination of _S. mutans_ Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC)  
Determination of MIC of HSs, EOs and 98% pure carvacrol (Sigma-Aldrich, Steinheim am Albuch, Germany) was carried out in sterile 96-well polystyrene microtiter plates (KiskerBiotech GmbH& Co. KG, Steinfurt, Germany). Bacterial cultures grown overnight in BHI broth were incubated under anaerobic conditions in an Anaerobic AG25, implementing the AnaeroGen Atmosphere Generation system (Oxoid, Basingstoke, UK), at 37 \({}^{\circ}\)C for 24 h. Resazurin sodium salt was used as an indicator of anaerobic conditions (Alfa Aesar, ThermoFisher GmbH, Munich, Germany) (30 mg/lt). Bacterial culture was adjusted to 0.5 McFarland turbidity standard (\(\sim\)1.5 \(\times\) 10\({}^{8}\) CFUs/mL). HSs were diluted in BHI broth at different concentrations ranging from 100% to 10% (\(v/v\)). EOs samples and carvacrol were diluted in sterile and distilled water with Tween-20 (BDH Chemicals Ltd., Poole, UK) at concentration 0.5% \(v/v\), then diluted in BHI broth at different concentrations ranged from 0.5% to 0.0175% (\(v/v\)). Subsequently, approximately 5 \(\times\) 10\({}^{4}\) CFUs/mL in 10 \(\mu\)L BHI broth was added to 190 \(\mu\)L of the tested diluted HSs, EOs and carvacrol and were incubated under anaerobic conditions at 37 \({}^{\circ}\)C for 24 h. Positive control wells containing BHI broth inoculated with bacteria tested the growth of the pathogen. Similarly, control wells containing 0.5% \(v/v\) Tween-20 and BHI broth inoculated with bacteria tested the growth of the pathogen in the presence of the detergent. Negative control wells containing hydrosols, EOs, carvacrol and Tween-20 dilutions in BHI broth without bacteria were included. Negative control wells containing only BHI broth were used to test for possible contamination. The MIC was determined as the lowest concentration which results in 100% growth inhibition [39]. MICs were determined in triplicate in at least two-independent experiments. The lowest concentration of any antibacterial agent that could kill the tested bacteria is considered the Minimum Bactericidal Concentration (MBC). The MBC was determined by transferring a small quantity of sample contained in each replicate well of the microtiter plates to BHI agar plates by using a microplate replicator (Boekel Scientific, Feasterville-Trevose, PA, USA). The plates were incubated at 37 \({}^{\circ}\)C for 24 h under anaerobic conditions [40]. Determination of _C. albicans_ Minimum Inhibitory Concentration (MIC) and Minimum Fungicidal Concentration (MFC)  
The susceptibility test of _C. albicans_ was performed based on the M27-A2 method [41] with some modifications. Determination of the minimum inhibitory concentration (MIC) of hydrosols and EO and carvacrol was carried out in sterile 96-well polystyrene microtiter plates (Kisker Biotech GmbH & Co. KG, Steinfurt, Germany). Fungal cultures were grown at 35 \({}^{\circ}\)C for 24 h in Sabouraud dextrose agar (Neogen, Lansing, MI, USA) plus chloramphenicol at 50 mg/L (Serva, Heidelberg, Germany). The inoculum was prepared by suspending _C.