This chapter deals with the formation of biofilms, their resistance to antibacterial agents, the importance and risk of biofilms, and nanotechnology methods for biofilm control in the food industry. Biofilm is a multi-layer cell cluster embedded in an organic polymer matrix, which protects microbial cells from environmental stress, antibiotics, and disinfectants. Microorganisms that live in contact points and the environment in food processing are mostly harmful because the microbial community in the wrong location can lead to contamination of the surfaces and products produced during the processing. When new nanomaterials (for example, silver or copper are incorporated) are used, the growth of surface biofilms can also be reduced. In recent years, new nanotechnology-based antimicrobials have been designed to kill planktonic, antibiotic-resistant bacteria, but additional requirements rather than the mere killing of suspended bacteria must be met to combat biofilm-infections.
TopIntroduction
Biofilm is a microbial community of extracellular matrix rich in polysaccharides. Microbial biofilm was first discovered in 1936. When a glass rod was added to the microbial solution, the adhesion of the microbial cell layer to the bottle wall and the biological activity of the suspension culture were significantly increased; subsequent research introduced the ubiquity of biofilm and planktonic microorganisms (Probert & Gibson, 2002). Various non-biological and biological surfaces, such as minerals, metals, animal or plant surfaces, lungs and intestines, as well as all types of medical implants are prone to bacterial colonization and biofilm formation. On the one hand, the advantages of biofilms have been applied in industrial processes. The microbial biofilmspose a huge risk, including chronic infections caused by these biofilms (R. M. Donlan & Costerton, 2002). Most importantly, biofilms are characterized by their resistance to biocides, antibiotics, and clearance caused by humoral or cellular host defense mechanisms (J. W. Costerton, Stewart, & Greenberg, 1999). Therefore, the use of traditional concentrations of bactericides or antibiotics is not effective in eliminating biofilms.
To control the risk caused by the formation of undesirable biofilms in the medical industry, it is necessary to formulate corresponding strategies to prevent and control the formation of biofilms. So, in this regard we need to fully understand the initial formation mechanism of biofilms, including attachment, development, maturation and detachment, and molecular level related regulatory process (Simoes, Borges, & Simoes, 2020). In fact, the microbes in the planktonic state hardly form biofilms, but the formation of biofilms occurs only in the presence of microbial groups (Berlanga & Guerrero, 2016). The strange thing is that the number of microorganisms that grow in planktonic growth is less than 0.1% of the total microorganisms (J. W. Costerton, Lewandowski, Caldwell, Korber, & Lappin-Scott, 1995). In general, the biofilm can be defined as an aggregated microbial community surrounded by an extracellular polymer (EPS) matrix, which develops on various inert or organic surfaces. Certainly, these biofilms are regulated by various physiological, environmental, and genetic factors. Admittedly, it is a very complex phenomenon, ranging from the structural characteristics of biofilms to various biofilm-related resistance mechanisms. Therefore, due to the complexity of biofilm formation and the antimicrobial resistance associated with biofilms, medical and industrial impacts are still difficult to control. Consequently, more research on biofilms is still needed in order to fully understand this phenomenon and to develop more effective methods for the prevention and eradication of these biofilms (Simoes et al., 2020).
Nevertheless, several speculations come about regarding the resistance of biofilm cells, including slow growth pattern of sessile cells, interaction of exopolymer with the antimicrobials, mutation, certain resistance genes expression, and the presence of a diffusion barrier to the chemicals posed by the glycocalyx, (Pace, Rupp, & Finch, 2005). In the natural ecological environment and pathogenic systems, bacterial biofilms are ubiquitous. The formation of biofilms can be beneficial or harmful. Many factors that affect the development of biofilms have been extensively studied, including the types of microorganisms, cell surface composition, surface, nutrition, fluid dynamics, and cell-to-cell communication.
Recently, by means of further understanding, the cell-to-cell communication in microorganisms, quorum sensing has become one of the most important mechanisms for controlling the development of highly structured biofilms on biological and non-biological surfaces. The resistance of biofilms to antibiotics often leads to the failure of chemotherapy and further refractory infections. In fact, biofilms are associated with more than 65% of all medical infections (Pace et al., 2005).