Chapter 10: Community Lifestyle of a Biofilm

Learning Objectives

  • Describe biofilm characteristics and formation

  • Differentiate biofilms from planktonic cultures

  • Explain features contributing to persistence and antimicrobial resistance in biofilms

  • Understand quorum sensing and chemotaxis in E. coli

  • Apply knowledge of E. coli systems to other bacteria

  • Interpret data on biofilms, quorum sensing, and chemotaxis

Bacteria and Biofilms

  • Biofilms are organized bacterial communities adhered to surfaces, surrounded by extracellular polymeric substances (EPS).

  • EPS consists of polysaccharides, proteins, and nucleic acids; biofilms can contain one or multiple species of bacteria.

  • Biofilm formation involves quorum sensing mediated by autoinducers leading to coordinated growth, maturation, and dispersion.

  • Planktonic bacteria are free-floating and can join or be part of a biofilm.

Prevalence of Biofilms

  • Biofilms account for 65-80% of bacterial infections; they can be benign or pathogenic.

  • Benign examples: environmental biofilms on surfaces (e.g., rocks, ships).

  • Pathogenic examples: biofilms on medical devices cause significant infections (e.g., urinary catheters, dental implants).

  • Chronic infections (e.g., cystic fibrosis) are often biofilm-associated.

Treating Biofilms

Antimicrobial Resistance

  • Biofilms exhibit >10,000 times more resistance to antibiotics compared to planktonic bacteria.

  • Key resistance factors: EPS matrix, nutrient/O2 gradients, presence of persister cells.

New Pharmaceutical Approaches

  • Strategies include interfering with EPS, inhibiting adherence, and targeting autoinducers.

Quorum Sensing

  • Quorum sensing allows bacteria to respond to population density using autoinducers to regulate gene expression.

  • In E. coli, the Lsr system regulates AI2 signaling, influencing community behaviors.

  • LsrR acts as a global regulator and is crucial for responding to AI2 concentration changes.

Bacterial Motility and Chemotaxis

  • Chemotaxis allows bacteria to navigate towards attractants or away from repellents.

  • Spatial and temporal sensing mechanisms enable bacteria to detect chemical concentration gradients.

  • E. coli motility involves runs and tumbles, with flagellar rotation directing movement.

Chemotaxis in E. coli

  • Involves chemoreceptors that, when activated by signals, alter flagellar rotation by phosphorylating response regulators like CheY.

  • Chemotactic responses include adjusting movement based on environmental cues, impacting interactions with chemicals.

Conclusion

  • Understanding biofilms, quorum sensing, and chemotaxis is crucial for addressing bacterial behavior in clinical and environmental contexts.