Pathway 15-4 Biofilm and Community-Based Microbial Pathogenesis

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Questions and Answers

What defines an ecosystem in the context of microbial communities?

A functional self-supporting system that includes the microbial community and its environment. (correct)

A habitat that solely supports one type of microorganism.

Only the microbial community itself.

The interactions between individual microorganisms.

Which aspect is NOT considered when determining the pathogenicity of a microbial community?

Geographic distribution. (correct)

Virulence factors.

Interaction types.

Abundance of species.

How does the community-as-pathogen concept differ from traditional views of pathogenicity?

It emphasizes the significance of vector-based transmission.

It focuses on individual species rather than interactions.

It considers only environmental factors.

It suggests the whole is more than just the sum of its parts. (correct)

What has community profiling revealed about the endodontic microbiota?

The bacterial composition varies between individuals with the same disease. Signup and view all the answers

What implication does the existence of differing community structures between disease forms suggest?

There are patterns associated with specific disease forms. Signup and view all the answers

Which characteristic is essential for biofilm architecture and its physiological functions?

Interactions among different microbial populations. Signup and view all the answers

⭐️What percentage difference in gene expression can occur between bacteria in biofilms and those in planktonic culture?

20% to 70% Signup and view all the answers

⭐️Which process allows bacteria within biofilms to coordinate their behavior and gene expression?

Cell-cell communication （quorum sensing) Signup and view all the answers

⭐️What factor contributes to the phenotypic heterogeneity observed in bacterial biofilms?

Gradients of environmental conditions Signup and view all the answers

What is one of the main characteristics of bacteria in biofilms compared to their planktonic counterparts?

Radically different phenotypes Signup and view all the answers

What process is primarily influenced by bacterial interactions occurring within biofilms?

Changes in gene expression Signup and view all the answers

What is primarily responsible for the structural integrity of a biofilm?

Extracellular polymeric substance (EPS) matrix Signup and view all the answers

⭐️What percentage of bacterial infections in developed countries is estimated to be linked to biofilm infections?

65% to 80% Signup and view all the answers

⭐️How do planktonic bacterial cells contribute to biofilm formation?

They attach to surface proteins and coaggregate with bound bacteria. Signup and view all the answers

⭐️What is the primary composition of the biofilm's extracellular polymeric substance?

Polysaccharides, proteins, and nucleic acids Signup and view all the answers

⭐️What factor significantly affects the antibiotic resistance of bacteria in biofilms compared to those in planktonic state?

The presence of a specialized subpopulation of persisters Signup and view all the answers

Which mechanism is NOT associated with the increased resistance of biofilm bacteria to antimicrobials?

Improved penetration of antimicrobial agents Signup and view all the answers

⭐️How much more antibiotic concentration is required to kill bacteria in biofilms compared to their planktonic counterparts?

100 to 1000 times higher Signup and view all the answers

What is a primary characteristic of bacteria in the stationary phase within a biofilm?

Lower susceptibility to antimicrobials Signup and view all the answers

Study Notes

Microbial Communities and Ecosystems

Individual microorganisms form populations, which can interact to create microbial communities within specific habitats.
These communities and habitats together form ecosystems, which are self-sustaining systems.
Dental plaque biofilms are sophisticated communities responsible for caries and periodontal diseases, impacting biofilm architecture and physiology with pathogenic consequences.
Apical periodontitis can also arise from biofilm communities established in the root canal system.

Community as Pathogen Concept

For numerous endogenous infections, microbial communities rather than single species are considered the unit of pathogenicity.
This "community-as-pathogen" concept emphasizes the collective behavior of bacteria in mixed infections, recognizing that the group's actions are more than the sum of individual species actions.

Factors Influencing Pathogenicity

The composition, abundance, interactions, and virulence factors of a microbial community collectively determine its pathogenicity and the resulting disease outcome.

Apical Periodontitis and Community Diversity

Studies indicate that the bacterial composition of the endodontic microbiota varies significantly between individuals with the same disease (apical periodontitis).
This suggests a heterogeneous etiology of the condition, where different combinations of bacteria contribute to disease development.
Interindividual variability in bacterial communities is even more pronounced when comparing different geographic locations.
The structure of microbial communities also differs noticeably between different disease forms of apical periodontitis, indicating a distinct pattern associated with each form (e.g., asymptomatic vs. acute apical abscess).

Biofilms and Bacterial Interactions

Biofilms are communities of microorganisms firmly attached to a surface, enmeshed in a self-produced matrix of extracellular polymeric substance (EPS), mostly composed of polysaccharide, but also proteins and nucleic acids.
Biofilms are essential for microbial survival in various environments, as they offer protection from external threats and support metabolic integration within the community.
Biofilm formation is considered a virulence factor, contributing to bacterial infections in humans, with an estimated 65% to 80% of infections in developed countries attributed to biofilms.
Biofilms are composed of populations or microcolonies embedded in the EPS matrix, separated by water channels, with dental biofilms reaching up to 300 cell layers in thickness.
The EPS matrix provides structural support, retains nutrients, water, and essential enzymes, and plays a role in adherence to surfaces.
In nature, bacterial populations within biofilms originate from planktonic (unattached) cells that colonize surfaces through attachment to host proteins or coaggregation with pre-existing bacteria.
In the root canal system, biofilm formation often occurs as a consequence of caries progressing towards the pulp, resulting in inflammation and necrosis, leading to biofilm formation on the root canal walls.
Bacterial interactions within biofilms lead to changes in growth rate, gene expression, and protein production, with a significant difference in gene expression compared to planktonic bacteria.
Biofilms utilize sophisticated cell-cell communication systems called quorum sensing to coordinate gene expression.
Phenotypic heterogeneity within biofilms arises due to exposure of microcolonies to gradients such as oxygen tension, pH, and nutrient variation, creating diverse microenvironments.

Biofilm Resistance to Antimicrobials

Biofilms exhibit significantly increased resistance to antimicrobial agents compared to planktonic bacteria.
The concentration of antibiotics required to kill bacteria within a biofilm is approximately 100 to 1000 times higher than that needed to kill the same species in a planktonic state.
There are several mechanisms contributing to biofilm resistance:
- The biofilm structure itself can act as a barrier, hindering the penetration of antimicrobial agents.
- Bacteria within biofilms often enter a stationary phase, characterized by slow growth and increased resistance to antimicrobials.
- A subpopulation of specialized survivor cells known as persisters exists within biofilms, exhibiting enhanced tolerance to antibiotics.

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