Biofilm Formation and Development

The bacterial biofilms are complex and structured microbial communities where the cells stick to one another and to surfaces and are imbedded by a self-produced extracellular polymeric substance (EPS) matrix. This way of life is quite opposite to that of planktonic (free swimming) bacteria which creates unique biological properties such as increased resistance to antibiotics and environmental stressors. The formation of biofilms is a universal survival mechanism used in a vast number of natural, industrial, and clinical systems, including the geologic and marine environments, as well as water pipelines and implanted medical devices (2). Biofilm formation is not an accident but a controlled developmental program which follows a series of steps, starting with a reversible adhesion of planktonic bacteria to a surface and ending with fully formed mature and organized communities where cells can be effectively detached and reattach in new niches. The company's internal processes are categorized into high-pressure, core processes, and support processes (27).

1. Initial Attachment

The initial stage of biofilm formation is interaction of free floating bacteria with any surface, which can be biotic (e.g., host tissues) or abiotic (e.g., metal, plastic or medical devices materials). At this point, the non-specific physical forces such as van der Waals forces, hydrophobic and electrostatic attractions between bacterial cell envelope and surface substrate dictate bacterial contact with the surface. This first attachment is generally reversible, cells are able to stick and unstick with ease when subjected to shear forces, or in response to environmental conditions (12). The surface structures of bacteria like flagella, pili and fimbriae contribute greatly, since they enable the motility and some adhesive contacts which reinforce the interaction with the surface. When the bacteria start to express cell surface adhesins and start to produce initial EPS components, the reversible adhesion is changed to a more permanent one (10).

2. Irreversible Attachment and Formation of Microcolonies

After the first contact, bacteria start to generate more EPS and increase its connection with the surface and starts to irreversible attachment. This is seen as the formation of a mono layer of adherent cells which are strictly attached using adhesive molecules and growing polymers . With permanent attachment, the individual cells multiply and start microcolonies- small groups of cells attached to an EPS scaffold which physically caters the community and traps nutrients. In these clusters, there is a high proximity between cells, and cell to cell communication is possible through quorum sensing (QS) a chemical signaling system that enables bacteria to perceive and react to changes in local population density through changes in gene expression patterns, especially those of EPS production, adhesion, and virulence. EPS is also a polysaccharide, protein, lipid and extracellular DNA (eDNA) which helps the biofilm to remain physically adherent, avoid exposure to environmental stress and antimicrobial resistance.

3. Biofilm Maturation

With increase in microcolonies, it transforms into mature biofilms with three dimensional structure with distinguishable structural features like channels and pores through which they transport nutrients, oxygen and metabolic waste. This complex structure is a result of the combination of cell growth, EPS generation and regulated gene expression under the control of the environmental signals and QS. The community also becomes more heterogeneous and complex in the process of maturation. Different depths of the cell have different microenvironment, i.e. nutrient, oxygen and waste product gradients, which induces phenotypic and metabolic differentiation in the biofilm. This heterogeneity plays an important role in biofilm resistance because cells in the deeper layers tend to go into a slow growth or dormant condition that is less vulnerable to antibiotics that act on active metabolism (Microbiology). It is also in biofilm maturation that there is the enhanced resistance to antimicrobials and host immune defenses when compared to the planktonic cells. The matrix of EPS serves as a barrier to diffusion and the changed gene expression and stress response systems increase the level of protection (7)

4. Quorum Sensing and Regulatory Mechanisms.

Quorum sensing and intracellular second messengers like cyclic di guanosine monophosphate (c di GMP) are also several factors that regulate the development of biofilms at the molecular level by suppressing flagellar motility and promoting adhesin and EPS synthesis. Stable attachment and matrix formation are stimulated by high c di GMP levels, whereas dispersal is induced by lower c di GMP levels (22). Quorum sensing requires the synthesis and perception of autoinducers, diffusible molecules, small in size, that display the concentration of local cell density. At a certain concentration, QS triggers biofilm special genes governing the synthesis of the matrix, sharing of protection by the community, and coordinated action within the community.

5. Dispersion

Dispersal is the last stage of biofilm life cycle where the cell loosens and falls off the mature biofilm to revert to the planktonic state and colonize other surfaces. The different environmental stimuli that cause dispersion include the depletion of nutrients, waste products accumulation, and variation of quorum sensing signals. Elements of the EPS are broken down by the enzyme and breaking the integrity of the matrix, groups of cells, or single bacteria escape (Royal Society of Chemistry). It is not some passive shedding but a controlled process that allows the populations of bacteria to expand and settle in new areas in the form of biofilms (35).

6. Clinical and Environmental Implications

The formation and development of biofilm in the environment, industry and clinics are of far reaching implications. Biofilms in natural ecosystems facilitate nutrient recycling and offer microbial communities adaptive benefits. Industrial systems Fouling, corrosion, and decreased efficiency of equipment such as pipelines and heat exchangers are all possible due to the growth of biofilms. Biofilms on medical equipment, as well as tissues, are linked to chronic infections because of their great resistance to antibiotics and immune systems evasion in clinical practice (3). Biofilms are complicated in structure and function which makes them very difficult to treat and manage. It is important to know the bio pathogenesis of biofilm formation, including attachment, EPS generation, maturation and dispersion, as well as the regulatory mechanisms involved, including quorum sensing and GMP signalling in order to come up with specific strategies to destabilize biofilms or prevent them completely (1).