Tissue-like community of bacterial cells adherant to some surface, enclosed in self-produced, protective polymeric matrix. Bacteria can grow safely in this protected environment.

Biofilms shield pathogens from phagocytes, antibodies, complement, and antibiotics.

Gingiva, foreign bodies (catheters, prosthetic implants).

Matrix binds antimicrobials and acts as a diffusion barrier.

Specialized metabolism: delegation of function in biofilm means only certain cells are replicating (dispersers), so static drugs are ineffective against cells that are metabolically inert (persisters, wall-formers)

Specialized microenvironments: within biofilm pH, O₂ levels vary; defense mechanisms/antibiotics won't be equally effective in every microenvironment.

Note: We typically test antibiotics on planktonic bacteria (bacterial suspensions), which are poor indicators of their efficacy against biofilms.

1. Attachment of motile cells

2. Secretion of polymer

3. Replication and differentiation

Note: Differentiation mediated by cyclic-di-GMP

4. Maturation of architecture: E.g. channels for nutrient flow, appendages for cell-cell communication

5. Spread to new sites: Motile cells disperse, or clumps of cells detach 

[image]

Microcolonies: clusters of bacteria surrounded by matrix. Note that biofilms are heterogeneous, made up of many different microcolonies (can be different bacterial species).

Channels: allow circulation of nutrients between microcolonies

Appendages: mediate cell-cell binding

Exopolysaccharide (matrix): outer coating of biofilm

Quorum-sensing molecules, aka autoinducers. E.g. Autoinducer peptide (AIP) in S. aureus.

Note: P. aeruginosa uses two quorum-sensing systems in series; threshold amount of first autoinducer will turn on second quorum-sensing system. Only Pseudomonas recognize first autoinducer, other species recognize second. (Not sure why that's important.)

Note: Pathogens can respond to autoinducers of other bacteria in the environment.

Intracellular signaling molecule that triggers biofilm formation.

Local cues (including quorum-sensing molecules) stimulate cyclic di-GMP, which:

-- Turns on genes for sessility, biofilm formation, and replication (e.g. adhesins)

-- Blocks transcription of motility and acute virulence genes (e.g. flagella)

Note: There are many such regulatory molecules (not proteins, not ribozymes) that affect gene expression. Mobley thinks this is particularly cool.

1. Give much higher doses (relatively unsuccessful, due to persister cells)

2. Design implants resistant to biofilm adhesion

3. Target matrix

4. Surgically remove biofilm

S. aureus

S. epidermidis

P. aeruginosa

H. influenzae

N. gonorrhoeae

... many others

Low levels of antibiotic degrade cyclic di-GMP, which allows persister cells to start expressing motility/virulence factors.

Note: Probably an evolutionary defense mechanisms against natural antibiotics.