Microbial_Primer_In_vivo_biofilm

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.