Biofilms - International Burch University
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Biofilms

Biofilms represent associations of microorganisms which are irreversibly connected to the surfaces by the production of an extracellular polymer substance (EPS) and at the same time show changed characteristics (phenotype), compared to the corresponding planktonic cells.


Accordingly biofilms are considered the next great challenge for microbiologists and clinicians especially taking into account their high rates of resistance towards antibiotics which makes them very difficult to treat.


Mr.sci. Monia Avdić


The „Gold Model“ for most microbiological examinations is the study of microorganisms in pure culture or the aqueous planktonic phase. However, the paradigm about planktonic bacterial cells does not reflect the real growth of bacteria in nature. Hence, during the last decade many studies were directed towards the understanding of bacterial growth in natural conditions. From these studies it is clear that many bacteria exist as part of a complex association attached to the surfaces and embedded in their own extracellular matrix. Today, such associations are more commonly known as biofilms. Biofilms represent associations of microorganisms which are irreversibly connected to the surfaces by the production of a extracellular polymer substance (EPS) and at the same time show changed characteristics (phenotype), compared to the corresponding planktonic cells. EPS is a highly dehydrated and chemically complex matrix which has the aim to store nutrients and at the same time can trap other microbes as well as non-cellular material like minerals, crystals and corrosion products. Inside a biofilm cells function coordinately as a cooperative consortium, in a way mimicking a multicellular organism. The process of developing this complex and highly differentiated association from single cells demands complex genetic regulation.


The formation of biofilms occurs in several consecutive phases. In the first phase an initial transport and reversible attachment of bacteria to the surface, with adsorbed organic and inorganic nutrients, takes place. Subsequently EPS gets secreted and it forms bridges between individual cells, which results in the irreversible attachment or „cementing“ of the cells to the surface. The last phase, in the formation of a biofilm, is the colonization of the surface. Bacteria, which are attached to the surface, grow and divide and by doing so create micro-colonies, which are regarded as the elemental organization units of biofilms. The “primary colonizer“ secrets substances which attract other planktonic bacteria that are found in the environment (secondary colonization). A completed biofilm has complex architecture and is made out of bacteria embedded in EPS coated micro-colonies, between which there are less dense parts of the matrix with permeable water channels that aid in the transport of nutrients and waste products.


The colonization of surfaces and subsequent formation of biofilms is best studied in bacteria, although fungi, algae, protozoa and viruses have been isolated from biofilms in the industrial and medical setting. Biofilms can form on almost all surfaces in the environment, irregardlessly weather the material is natural (plant and animal) or synthetic (medical indwelling device and industrial surface).


In humans biofilms can have a protective role. For example the gut commensal flora forms biofilms which are attached to epithelial cells, making a barrier which prevents the penetration of pathogens. Dental plaque is made out of different bacterial biofilms, but the decline of teeth is a consequence of proliferation of pathogenic strains in the same. Although biofilms are ubiquitary in nature, their significance in the clinical setting is often underestimated. Today biofilms represent a severe source of infection, especially in immunocompromised individuals with indwelling medical devices (like catheters). This has serious clinical consequences and is the cause of many persistent and chronic infections. Thereby one should have in mind that bacteria inside a biofilm are embedded inside EPS which provides them protection from the hosts immune response as well as antimicrobial remedies. Infections caused by biofilms often have recurring symptoms until the source of the infection is not removed surgically. In opportunistic pathogens, like Staphylococcus epidermidis, the ability to form biofilms is considered a factor of virulence and so commensal bacteria become a severe source of infection in the hospital environment. Today numerous studies confirmed that the rates of horizontal gene transfer are elevated in biofilms compared to planktonic bacteria. Inside biofilms horizontal gene transfer is responsible for the appearance of antibiotic resistance which can pass from commensal to pathogenic bacteria. It is considered that the “notorious MRSA” gained the mecA gene, which is responsible for the resistance to methicillin, through horizontal gene transfer.


Accordingly biofilms are considered the next great challenge for microbiologists and clinicians especially taking into account their high rates of resistance towards antibiotics which makes them very difficult to treat.


Literature

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  3. Hall-Stoodley, L., Costerton, J. W., & Stoodley, P. (2004). Bacterial biofilms: from the natural environment to infectious diseases. Nature Reviews Microbiology, 2(2), 95-108.
  4. Madsen, J. S., Burmølle, M., Hansen, L. H., & Sørensen, S. J. (2012). The interconnection between biofilm formation and horizontal gene transfer. FEMS Immunology & Medical Microbiology, 65(2), 183-195.
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