Biofilm

Staphylococcus_aureus_biofilm

5 stages of biofilm development. Stage 1, initial attachment; stage 2, irreversible attachment; stage 3, maturation I; stage 4, maturation II; stage 5, dispersion.

Biofilm is a structure formed by bacteria which serves for their adherence, communication and protection. It can also be a factor in pathogenicity and virulence. It adheres to inert or inorganic surfaces (wet surfaces in nature, implants, catheters, cannulas) and living (epithelial cells). It is a complex structure with channels (water brings nutrients and removes waste). Reminiscent of tissues of higher organisms. usually contribute to its formation.

Biofilm increases the resistance of bacteria (to adverse environmental conditions or immune mechanisms) and allows for their rich communication, which can greatly complicate treatment.

Biofilm formation

The adhesion of bacteria to the surface (using fimbriae, glycocalyx, surface proteins, etc.) conditions the triggering of genes for the formation of extracellular polymers. Additional cells form in the extracellular Polysaccharide mass. Dividing creates so-called microcolonieswhich grow rapidly. The microcolony is enveloped in mucus and differentiates into a biofilm. They can be formed not only by bacteria, but also by higher organisms (e.g.Candida albicans in the body). Free cells (planktonic cells)can be released from the biofilm and colonize other sites.

Communication of bacteria through biofilm consists mainly in the exchange of genetic information (e.g. plasmids) between bacteria. In this way, bacteria can, for example, acquire resistance to antibiotics.

Quorum sensing

The mechanisms by which bacteria can sense and adapt to the presence of other bacteria in their environment. During their growth, bacteria produce so-called autoinductors. When the concentration of autoinductors reaches the threshold concentration, the transcription of the genes of the multiplying bacteria is affected. By this change in gene expression, they can condition growth arrest bacteria or their further growth. By this mechanism, the colony maintains an optimal population density.

Another factor that autoinductors may affect is the production of some metabolites (e.g. the production of proteases in Pseudomonas aeruginosa).

The biofilm can be observed with a confocal laser microscope in optical sections and the spatial structure can be composed of them. Biofilm thickness varies from a few to hundreds of micrometers, depending on nutrient availability.

Examples of biofilm formation sites

• Dental plaque – viridizing streptococci.
• Periodontitis – in the pockets under the gums (formation of a polymicrobial biofilm where oxygen does not penetrate), accumulated bacterial mass, dead cells and purulent cells worsen the situation.
• Inflammation of the middle ear – Haemophilus.
• Osteomyelitis – Staphylococcus aureus;
• Cystic fibrosis chronic or recurrent infections are added to primary respiratory infections. Bronchial congestion and permanent epithelial damage occur. Pseudomonas aeruginosa and the like settle on this damaged epithelium with a biofilm.
• Inflammation of the bile ducts – G− intestinal stick.
• With chronic prostatitis - bacteria enter the prostate upstream, acute prostatitis can turn chronic. Initially, biofilm is just a complication, later the cause of the disease.
• Poorly nourished skin and subcutaneous tissue in shin ulcers, on the surface of burned areas.
• The intrauterine device can cause inflammation of the pelvic cavity and sepsis.
• Assisted breathing - formation on the wall of tubes. In case of lack of treatment, bacteria can penetrate into the bronchi and lungs.
• Intravenous catheters – coagulase negative staphylococci.
• Artificial heart valves.
• Joint replacements.
• Contact lenses − if used incorrectly Pseudomonas aeruginosa settles.
• In urology, biofilm is the most common cause of infection with a urinary catheter inserted.

Biofilm resistance to antibiotics

Biofilm cells are very resistant to antimicrobials and disinfectants (up to a thousand times more than planktonic cells). In medical practice, this means that even high doses of antibioticsare not enough for treatment . Resistance is expressed phenotypically - it is not genetically determined resistance.

Laboratory tests for antibiotic susceptibility give incorrect results. Biofilm bacteria are resistant, but compared to planktonic bacteria, they appear sensitive under optimal laboratory conditions.

The resistant cells that tolerate the antibiotic and remain in the body are generally called persists. In a biofilm, genes are up to a thousand times more successful between cells than between planktonic cells (promoting resistance gene transfer in the population). The mucus mass also physically protects the cells in the biofilm from antibodies.

Links

Related articles

• Bacterial multiplication in vitro

References

• SCHINDLER, Jiří. Microbiology for medical students. 1st edition. Praha : Grada, 2010. ISBN 978-80-247-3170-4.

Source

• JANSKÝ, Petr. Processed questions from microbiology [online]. [cit. 2012-02-06]. <https://www.yammer.com/wikiskripta.eu/uploaded_files/3804405>.