What are biofilms?

What Are Biofilms?

Biofilms are structured communities of microbial cells (bacteria or fungi) that are firmly attached to surfaces or aggregated together and encased in a self-produced extracellular polymeric matrix composed of polysaccharides, proteins, extracellular DNA, and lipids. 1

Structural Composition

The biofilm matrix—termed the "matrixome"—consists of multiple components that work together to create a protective environment: 2

• Extracellular polymeric substances (EPS) form the structural backbone, including polysaccharide intracellular adhesin in Staphylococcus species that promotes adhesion to surfaces 1
• Host-derived components such as fibrin, platelets, fibronectin, collagen, and immunoglobulins become integrated into the matrix structure 1
• Extracellular DNA provides structural stability, facilitates gene transfer between cells, and supplies nutrients to the biofilm community 1
• Proteins and lipids contribute to matrix cohesion and protect against environmental stresses 3

Formation Process

Biofilm development occurs through distinct sequential stages: 1

1. Initial attachment: Bacteria adhere to surfaces through physicochemical forces (hydrophobicity, surface tension, electrostatic charge) and specific bacterial surface adhesins called MSCRAMMs (microbial surface components reacting with adherence matrix molecules) that bind to host proteins like fibronectin and collagen 1

2. Microcolony formation: Adherent bacteria multiply and stick to one another, forming small colonies through polysaccharide intracellular adhesin-mediated cell-to-cell adhesion 1

3. Biofilm maturation: Bacterial clusters grow into tower-like structures embedded in the expanding extracellular matrix 1

4. Dispersal: Planktonic cells are released to colonize new sites 1

Biofilms can develop remarkably quickly—within 10 hours of wound contamination in chronic wounds 4

Size and Detection Challenges

Biofilms are typically microscopic in vivo, measuring only 4-200 μm in tissues and 5-1200 μm on foreign bodies, making them difficult to detect without specialized techniques. 4 This small size explains why biofilms often go unrecognized clinically despite their prevalence (80-90% of chronic wounds contain biofilm). 4

Unique Physiological Properties

Bacteria within biofilms undergo a phenotypic shift from their planktonic (free-floating) counterparts, involving large-scale gene regulation changes: 1

• Physiological and biochemical gradients exist from the surface to deeper layers of the biofilm structure, creating zones with different nutrient availability, oxygen levels, and growth rates 1
• Enhanced antimicrobial resistance: Microbes in biofilms are significantly more resistant to antibiotics and host immune defenses compared to planktonic cells, likely due to the dense extracellular matrix protecting organisms in the biofilm interior 1, 5
• Small colony variants represent phenotypic variations that enhance staphylococcal survival within biofilms and confer resistance to certain antibiotics 1
• Polysaccharide intracellular adhesin-positive bacterial strains demonstrate greater antibiotic resistance than adhesin-negative strains 1

Clinical Significance

Biofilms function as "protective clothing" for microorganisms, shielding them from: 6

• Antimicrobial agents and antibiotics 1, 5
• Host immune system responses (both innate and adaptive) 1, 5
• Extreme environmental conditions including UV radiation, temperature extremes, pH variations, and high salinity 6

Biofilm infections are characterized by persisting and progressive pathology due primarily to the inflammatory response surrounding the biofilm, making them difficult to diagnose and treat efficiently. 1 This explains why biofilm-associated infections become chronic and resistant to standard antimicrobial therapy.

Common Clinical Contexts

Biofilms occur in two main settings: 1

• Tissue-associated biofilms: Cystic fibrosis chronic lung infections, chronic wound infections 1, 4
• Device-associated biofilms: Cardiovascular implantable electronic devices, orthopedic implants, endotracheal tubes, intravenous catheters, indwelling urinary catheters 1

Critical Management Pitfall

Antimicrobial dressings or antibiotics alone without mechanical disruption of the biofilm structure are inadequate for treatment. 4 The protective matrix must be physically disrupted to expose bacteria to antimicrobial agents, as the biofilm architecture itself confers resistance independent of bacterial genetic resistance mechanisms.