Applications of Atomic Force Microscopy and Optical Tweezers in Probing Bacterial Adhesion

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Applications of Atomic Force Microscopy and
Optical Tweezers in Probing Bacterial Adhesion

• By Benjamin R. Lundgren

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Bacterial adhere to mucosa and subsequently cause
tissue damage (infection)
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Bacterial cell adhesion principles

• Possess several adhesion molecules, adhesins,
  that recognize distinct host-cell receptors
• Adhesins display tropisms
• Although adhesins can vary considerably in
  binding affinities and amino acid sequence, they
  do share some structural similarity
• Mimic eukaryotic cell-adhesion molecules

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Bacterial Lectins

• Lectins proteins that recognize and bind to
  carbohydrates
• Present in most organisms
• Polyvalent in nature, which enables tight binding

Many adhesins are lectins
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Understanding Bacterial Adhesion

• Bacteria use hundreds of molecules in binding to
  host cells
• Probing individual adhesin-receptor adhesive
  forces enables researchers to discriminate
  between minor and major adhesion events
• Bacterial adhesion is vital for biofilm
  development
• Single-molecule techniques such as AFM and
  optical tweezers are attractive methods for
  examining bacterial adhesion

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Measuring forces with AFM
Common approach for comparing adhesion forces
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M. xanthus biofillm
Mounds are multi-layered sheets of xanthus
cells Mound edges represent single-layer of
cells Pili extend from poles of cells
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Role of fibrils (extracellular polysaccharidespro
tein matrix) in gliding
Li, Y. Sun, H. Ma, X. Lu, A. Lux, R. Zusman,
D. Shi, W. Extracellular polysaccharides
mediate pilus retraction during social motility
of Myxococcus xanthus. PNAS, 2003, 100, 54435448.
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Analyzing dynamics between bacterium and cognate
host-cell receptor with AFM
Variation of loading rates enabled the formation
of an energy landscape
Firm Adhesion vs. Transient Adhesion
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Optical tweezers in determining bacterial-adhesin
determinants
Analyzed mutant adhesins abilities to bind to
common host-cell receptor
Adhesin domains required for binding were
determined according to their respective rupture
forces
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Anti-adhesive therapy in bacterial pathogenesis
Analogs for either adhesin or adhesin-receptor
are promising for reducing bacterial infection