What are biofilms?

What Are Biofilms?

Biofilms are structured communities of microbial cells that adhere to surfaces and become encased in a self-produced extracellular polymeric matrix composed of polysaccharides, extracellular DNA, proteins, and lipids. 1

Structural Composition and Formation

Biofilms develop through a sequential process that transforms individual planktonic bacteria into organized microbial communities:

• Initial adhesion occurs through both passive mechanisms (electrostatic interactions, Van der Waals forces) and active mechanisms (adhesin-mediated binding to surface proteins like fibronectin and collagen) 1
• Microcolony formation follows adherence, where bacterial cells interact and cluster together, promoting biofilm development 1
• Maturation phase produces massive bacterial clusters called "towers" within a polymeric framework 1
• The extracellular matrix contains polysaccharide intracellular adhesin, extracellular DNA (which supplies nutrients and transfers resistance genes), lipids, and proteins 1

Clinical Significance and Impact

The clinical importance of biofilms cannot be overstated, particularly in healthcare settings:

• 80-90% of chronic wounds contain biofilm, which can develop within 10 hours of wound contamination 2
• Biofilms are implicated in device-related infections affecting catheters, pacemakers, prosthetic devices, contact lenses, and cardiovascular implantable electronic devices 1, 3
• Biofilms measure 4-200 μm in tissues and 5-1200 μm on foreign bodies, making them difficult to detect without specialized techniques 2
• The first documented evidence of biofilm involvement in device-related infections came from a 1982 electron microscopy examination of a pacemaker lead infected with Staphylococcus aureus 1

Antibiotic Resistance Mechanisms

Biofilms confer extraordinary resistance to antimicrobial agents, requiring antibiotic concentrations 100-1000 times greater than those needed to kill planktonic bacteria. 3

The resistance mechanisms include:

• Physical barrier protection from the extracellular polymeric matrix that restricts antibiotic penetration 1, 4
• Altered bacterial growth rates within the biofilm structure that reduce antibiotic efficacy 5
• Gene transfer capabilities facilitated by extracellular DNA, which stabilizes the matrix and spreads resistance traits 1
• Protection from host immune defenses through impaired phagocyte activation and complement system function 5
• Polysaccharide intracellular adhesin-positive bacterial strains (such as S. epidermidis and S. aureus) demonstrate significantly greater antibiotic resistance compared to adhesin-negative strains 1

Common Biofilm-Producing Pathogens

Key organisms responsible for biofilm-associated infections include:

• Staphylococcus epidermidis produces extensive extracellular slime (polysaccharide intercellular adhesin) that forms biofilms on medical devices 3
• Staphylococcus aureus forms biofilms using surface adhesins (MSCRAMMs) and has been linked to methicillin-resistant and vancomycin-resistant strains 3, 5
• Pseudomonas aeruginosa produces metallo-beta-lactamase and forms biofilms in chronic infections like cystic fibrosis 5
• Candida species create structurally distinct biofilms that require specialized detection methods 3

Clinical Pitfalls and Management Considerations

The most critical pitfall is mistaking slough (necrotic debris) for biofilm, which leads to inappropriate treatment strategies. 2

Important management principles:

• Antimicrobial dressings alone are inadequate without mechanical disruption of the biofilm structure 2
• Device removal is often necessary for biofilm-associated infections, as antibiotics alone cannot eradicate bacteria protected within the matrix 3
• Each log10 increase in bacterial count within biofilm-containing wounds is associated with a 44% delay in healing time 2
• Treatment typically requires surgical device replacement combined with prolonged antibiotic therapy, incurring substantial healthcare costs 6

Biofilm Distribution in Clinical Settings

Biofilms cause infections across multiple body systems:

• Chronic otitis media, sinusitis, tonsillitis, and laryngitis 1
• Endocarditis and lung infections in cystic fibrosis 1
• Urinary tract infections and kidney stones 1
• Osteomyelitis and chronic wounds 1
• Dental plaque and biliary tract infections 1