## 1 Introduction  
Biofilm is a diversified and adaptive community of microbial cells that displays a high tolerance to conventional antimicrobials (antibiotics, antiseptides, disinfectants) due to the presence of a protective extracellular matrix, diversification of metabolism within specific biofilm layers, and coordinated reactivity to stimuli [1]. High tolerance to stressors and antibiotic resistance mechanisms displayed by microbial cells within the biofilm make the structure highly persistent and are the reasons why science has recognized the biofilm's central role in the pathogenesis of infective diseases [2; 3; 4]. Such opportunistic pathogens as _Staphylococcus aureus_, _Pseudomonas aeruginosa_, and _Candida albicans_ are particularly frequently associated with serious biofilm-related infections and strong antibiotic resistance [5]. The health complications resulting from infections caused by the above-mentioned pathogens are of severe and life-threatening nature. Moreover, they are also a significant economic burden for healthcare systems [6]. Therefore, the introduction of novel antibiofilm countermeasures is one of the most pressing needs of contemporary medicine [7]. The use of such antimicrobial substances of plant origin as essential oils (EOs) in biofilm eradication is considered a promising direction to follow [8]. Thanks to their high lipophilicity, EOs bind to and break the integrity of microbial cell walls and membrane structures, which results in cell lysis through a mechanism resembling the one displayed by antiseptides [9]. Moreover, individual EOs are characterized by low toxicity, a broad spectrum of effectiveness, biodegradability, as well as anti-inflammatory and immune-stimulating properties [10]. The above-mentioned features also predispose EOs to be used either in monotherapy or as adjuvant substances for antibiotics [11]. We have chosen the essential oils of confirmed biological activity, including eucalyptus oil (_Eucalyptus globulus_ [PERSON]), which exhibits antibacterial, antifungal, analgesic, and anti-inflammatory properties and has also been widely used in pharmaceutical, food, and cosme products [12]; thyme oil (_Thymus vulgaris_ L.), which is known for its anti-inflammatory and antibacterial properties [13], and tea tree oil (_Melaleuca alternifolia_ [PERSON]), which is employed largely for its antimicrobial properties and incorporated as an active ingredient in many topical formulations used to treat cutaneous infections [14]. Both liquid and volatile fractions of EOs may display antimicrobial (and antibioofilm) activity. However, while the testing methods for EOs liquid fractions rely on well-defined EUCAST (European Committee for Antimicrobial Susceptibility Testing) and pharmacopeial recommendations [15; 16], the methodology of testing EOs' volatile activity against microbes is highly diversified. These differences concern not only the experimental setting itself but also the various types of microbial aggregates scrutinized (lawn, biofilm) [17; 18; 19]. Moreover, also, the EOs are highly intra-species differentiated (with regard to the composition and concentration of antimicrobial compounds) caused by geographic and location factors, seasonal effects, and genetic factors, which determine the so-called chemotypes commonly found in EO-bearing plant species [20]. The above may explain why various scientific studies of the activity of the same type of EO against the same microorganism obtained using a single testing method produce varying data [21; 22]. Such a lack of standardization impedes the introduction of EOs to the ensemble of clinical, anti-infective measures. Since there is an urgent need for new \"anti-biofilm\" compounds, the development of an in vitro test for screening the antibiofilm activity of volatile fractions of EOs is of high importance.