# Antibiofilm Potential of Natural Essential Oils
## 2 Biofilm: The Role in the Pathogenesis of the Disease  
Microorganisms (bacteria, fungi, protozoa) become increasingly resistant to physical and chemical factors due to their association in the form of a specific biological membrane called a biofilm (BF). BFs are ubiquitous in the natural environment. They are formed by bacteria in natural and industrial systems as part of their survival strategy, which protects them against AM chemical substances, environmental bacteriophages, and phagocytes. BFs are resistant to extreme conditions and are capable of protecting microorganisms against UV radiation, high pressure, or nutrient deficiency [5]. They represent a complex, cross-linked structure, the components of which affect many of their properties, like hydrophobicity and reduced gas permeability [6]. BF formation is regulated by genetic and environmental factors, and the main stages of this process include the attachment of microorganisms to a solid surface, enhanced production of the extracellular polymeric substance (EPS), and BF detachment (Figures 1 and S1). The balance between BF attachment, growth, and detachment is important in the formation and maintenance of a functional community [7]. In a BF, microbial cells are connected to each other by EPS containing polysaccharides (the largest fraction), proteins, nucleic acids, surfactants, lipids, and water [8]. BFs are of great importance to public health as their development is one of the key mechanisms of bacteria resistance to AM agents [6]. According to data from the National Institutes of Health, USA, BFs are responsible for almost 80 types of infections induced by microorganisms and 65 types of hospital infections [9]. The infections caused by BF-producing bacteria include such conditions as, e.g., cystic fibrosis, otitis media, infectious endocarditis, and chronic inflammatory diseases [10]. Bacterial BFs are found on wound surfaces, are implicated in wound healing failure, and contribute to the chronic inflammatory condition. _Pseudomonas aeruginosa_ can be a major contributor to wound inflammation due to the production of rhamnpids [11]. Recent meta-analyses have shown the likely involvement of BFs in the pathogenesis of atherosclerosis. The presence of BF has also been speculated to contribute to an increased risk of atherosclerotic plaque rupture [12]. Bacteria and fungi have the ability to estimate their own density in a given environment due to the quorum sensing phenomenon (QS), which is a process of chemical communication between bacterial cells,  
Figure 1: Subsequent stages of biofilm formation. affected by the bacterial population density and mediated by small signaling molecules called autoinducers. Microorganisms synthesize and secrete signaling substances into the environment. One of the tasks of these substances is to coordinate the control of the expression of genes involved in BF formation. The traits of bacteria regulated by QS include, among other things, virulence, BF formation, sporulation, genetic competence, and bioluminescence [13]. QS allows the bacteria to monitor the environment in terms of the presence of other bacteria and to adjust their behavior at the entire population scale in response to changes in the number and/or species composition of a bacterial community [14]. The QS phenomenon may occur in both Gram-positive and Gram-negative bacteria as well as in fungi (e.g., _Candida albicans_) [6; 15]. _Biological Profile of Biofilm_  
BF is formed by a multicellular community, often heterogenous in terms of species and featuring a spatial character. It may include from one to several, or even a dozen different species. This structure is formed not only within representatives of the same kingdoms, as interspecific and intergenic BFs are also likely, e.g., _S. mutant_ and _C. albicans_[16]. [PERSON] and [PERSON] [17] have isolated 67 bacteria from food products sold at the market, of which seven were strong and two were moderate BF producers (_Enterococcus faecalis_, _Bacillus cereus_, _C. freundii_, _S.