Page 1: Introduction to Biofilms

Authors and Affiliations

• Kendra P. Rumbaugh, Texas Tech University Health Sciences Center, Lubbock, Texas, USA

• Thomas Bjarnsholt, University of Copenhagen, Copenhagen, Denmark

Abstract

• Overview of biofilms and their implications in infections.

• Historical perspective starting from Van Leeuwenhoek to Bill Costerton.

• Challenges in replicating biofilm infections in laboratory settings.

• In vivo analyses reveal biofilm structure, composition, and behaviour but gaps in knowledge persist regarding infection initiation, diversity, and the infectious microenvironment (IME).

Key Concepts

• Microbial History: Recognizing the longstanding understanding of microbes as both individual cells and aggregates (biofilms).

• Bill Costerton's Contribution: Established the link between biofilms in nature and human infections, highlighting their tolerance to antibiotics.

• Terminology: The term 'biofilms' was coined to describe aggregated bacteria on surfaces.

Importance of Biofilms

• Clinical Significance: Biofilms are critical in understanding chronic and recurrent infections as they evade host defences and antibiotics.

• Evolution of Perspectives: Early beliefs confined biofilms to attached surfaces; now includes suspended aggregates and host-derived components.

Concluding Thoughts

• Biofilm research is vital in disease management, requiring continuous exploration to fully understand their complexity in clinical scenarios.

Page 2: Hallmark Characteristics of In Vivo Biofilms

Structural Differences

• Size Variation: In vivo biofilms are generally smaller and lack the complex architecture seen in lab-grown biofilms.

• Aggregate Sizes: Biofilms associated with foreign bodies average about 1200µm, while tissue infections consist of smaller aggregates (5–200µm).

Emergent Properties

• Antibiotic Tolerance: A significant feature of biofilms attributed to their matrix and altered cell physiology.

• Matrix Composition: Extracellular polymeric substance (EPS) includes host proteins and is less understood in vivo.

Physiological Adaptations

• Host-Dependent Factors: In vivo biofilms may exhibit unique behaviours and metabolic pathways due to host interactions, influencing their vulnerability to antibiotics.

• Nutrient and Oxygen Availability: In vivo conditions differ significantly from lab environments, further complicating biofilm behaviour understanding.

Page 3: Modeling In Vivo Biofilms

Development of Models

• Various models developed over five decades using both invertebrate and mammal hosts.

• Host selection involves considerations of cost, ethics, anatomy, and the specific disease being studied.

Types of Models

• Foreign-Body Models: Simulate infections related to implanted objects, like catheters.

• Tissue Infection Models: Focus on chronic infections related to wounds or internal tissues, helping understand biofilm-related conditions.

Challenges

• Ethical concerns and costs significantly affect mammalian studies.

• Individual variability in animal responses can complicate study outcomes.

• Inoculum Size: In vivo models often begin with artificially high infection loads, which may not reflect realistic human infection scenarios.

Page 4: Analyzing In Vivo Biofilms

Methods and Techniques

• Imaging: Real-time tracking of biofilm dynamics using bioluminescent bacteria or advanced microscopy techniques like CLSM.

• Histopathology: Allows visualization of tissue impact and assessment of inflammation due to biofilm infection.

Quantifying Bacterial Load

• Techniques such as qPCR and culture-based methods help assess infection severity and bacterial responses to treatments.

Multidisciplinary Approaches

• Techniques for transcriptomics and proteomics provide insights into biofilm adaptability and host interactions, essential for understanding biofilm pathogenesis.

Page 5: Gaps in Knowledge and Future Directions

Understanding Infections

• Infections likely begin when opportunistic bacteria exploit environmental breaches, but the exact initiation process remains poorly understood.

• The ability of a minimal bacterial load to sustain infections is unclear.

Bacterial Diversity

• Knowledge of bacterial diversity in infections is limited; some infections are predominantly mono- or polymicrobial with varying interactions.

The Infectious Microenvironment (IME)

• The IME's complexities affect bacterial survival and antibiotic efficacy, requiring further research to improve treatment strategies.

Conclusion

• The field of biofilm research in infections is dynamic, necessitating ongoing study to enhance understanding, prevention, and treatment of biofilm-related diseases.