Microbiology
Biofilm
Bacterial communities embedded in self-produced matrix — most bacteria live this way
A biofilm is a community of microorganisms (mostly bacteria) attached to a surface and embedded in self-produced extracellular polymeric substance (EPS) — slime made of polysaccharides, proteins, DNA. Most bacteria in nature live as biofilms (~80%), not as planktonic (free-floating) cells. Examples: dental plaque, kitchen counters, water pipes, medical implants. Properties: highly resistant to antibiotics (1000× more than free-living), share resources, communicate (quorum sensing). Cause: chronic infections, contamination, biofouling. Important target: anti-biofilm strategies in medicine, industry.
- DefinitionBacterial community in EPS matrix attached to surface
- CompositionCells + polysaccharides, proteins, eDNA
- % of bacterial life~80% as biofilms
- Antibiotic resistance100-1000× more than planktonic
- ExamplesDental plaque, water pipes, implants
- Discovery nameCoined by Costerton (~1978)
Interactive visualization
Press play, or step through manually. The visualization is yours to drive — try it before reading on.
Watch the 60-second explainer
A condensed visual walkthrough — narrated, captioned, under a minute.
Why biofilms matter
- Disease. Many chronic infections.
- Industry. Biofouling of pipes, equipment.
- Medicine. Implant infections, cystic fibrosis.
- Dental. Plaque and tooth decay.
- Environment. Wastewater treatment, bioremediation.
- Microbiology. Most natural bacterial behavior.
- Drug development. Need biofilm-targeting drugs.
Common misconceptions
- Biofilm = single species. Often multi-species.
- Bacteria live as free cells. Most live as biofilms.
- Biofilms simple aggregates. Highly organized, structured.
- Antibiotics work same way on biofilms. Much less effective.
- Biofilms only on surfaces. Some float (e.g., flocs).
- EPS is just glue. Provides protection, signaling, etc.
Frequently asked questions
How does biofilm form?
Stages. (1) Reversible attachment: planktonic bacteria contact surface. (2) Irreversible attachment: secrete EPS; firmly adhere. (3) Microcolony formation: cells multiply locally. (4) Maturation: 3D structure develops; channels for nutrient/waste flow. (5) Dispersion: cells released to colonize new locations. Whole process: hours to days. Different bacteria can join same biofilm — multispecies communities.
What's quorum sensing?
Bacterial communication via chemical signals. Cells secrete autoinducers (small signaling molecules); sense local concentration. When threshold reached (= high cell density): coordinated gene expression. Triggers: virulence factor production, biofilm formation, bioluminescence (Vibrio). Different signal molecules for different species; some cross-species. Discovered 1970s. Disrupting QS: anti-biofilm strategy.
Why are biofilms antibiotic-resistant?
Multiple mechanisms. (1) Reduced antibiotic penetration through EPS. (2) Persister cells: dormant cells in biofilm, less affected. (3) Slow growth: many antibiotics target growing cells. (4) Altered gene expression: some genes upregulated in biofilm. (5) Horizontal gene transfer: easy in biofilm; spread resistance genes. Result: 100-1000× more resistant. Cause many chronic infections.
What are common biofilm infections?
(1) Dental plaque/caries: oral biofilm. (2) Endocarditis: heart valve biofilm. (3) Otitis media: ear infections. (4) UTIs: bladder catheters. (5) Lung infections in cystic fibrosis: Pseudomonas. (6) Medical implants: catheters, prostheses, contact lenses. (7) Wound infections. Difficult to treat; often require physical removal.
Are biofilms always harmful?
No. Many beneficial. (1) Gut microbiome: provides services to host. (2) Sewage treatment: biofilms degrade waste. (3) Bioremediation: cleaning oil spills. (4) Industrial fermentation. (5) Nitrogen fixation in soil. (6) Microbial mats in extreme environments. Both beneficial and harmful applications. Goal: encourage useful biofilms; prevent unwanted.
How are biofilms studied?
Various methods. (1) Confocal microscopy: 3D imaging with fluorescent stains. (2) Flow cells: simulate biofilm growth conditions. (3) Microfluidics: controlled environments. (4) Genomics: which genes expressed in biofilm. (5) Proteomics: protein production. Real-time imaging of biofilm formation revealed complexity. Many discoveries relatively recent (1990s+).
What anti-biofilm strategies exist?
Several. (1) Surface modification: prevent attachment (silver, copper, micro-textured). (2) Quorum-sensing inhibitors: prevent signaling. (3) Biofilm dispersers: trigger release of cells. (4) Mechanical removal: cleaning, debridement. (5) Bacteriophage therapy: phages can kill biofilm bacteria. (6) Anti-EPS enzymes: dispersin breaks down matrix. Active research area.