2. Biofilms
• Layman terms – Bacteria can join together on any surface & start to form a protective
covering around their group.
• Microbially derived sessile community consists of cells irreversibly attached to a
substratum
• Embedded in a matrix of extracellular polymeric substances produced by them
• Exhibit altered phenotype w.r.t growth rate & gene transcription
• Significance: Protect and allow bacteria to survive and thrive in hostile environments
• Withstand host immune responses, much less susceptible to antibiotics and
disinfectants
• Animalcules are observed by Anton Von Leeuwenhok from the biofilms of his dental
plaque
• Research in biofilms begin after 1980s.
4. Biofilms
IMPORTANT FACTORS IN BIOFILM FORMATION
Cell attachment
Extracellular polysaccharides (EPS)
Cell-cell communication (Quorum sensing)
Cell attachment
• Cell surface hydrophobicity : bacterial attachment to
each other & to surfaces – interaction of hydrophobic
domains
Extracellular filamentous appendages in biofilm formation
• Flagella : transport , initial cell-surface interactions
• Pilli / fimbriae : adherence to bacterial cells and
inorganic particles
• Prostheca / Stalks : attachment factors in microbes
• At the end is an adhesive disk ‘Holdfast’ – attachment
to surfaces
5. Basic units of biofilm: microcolonies of homogenous
and heterogenous bacterial species. Microbial cells – 15 % ; Matrix material -85 %
EPS : polysaccharides, proteins ( 75-90%) nucleic acids, lipds, phospholipids & humic
substances
Role of EPS in biofilms
Acts as a barrier – only diffusion transport is possible
Delays / prevents antimicrobials passage due to barrier effect or chemical interactions
Cell-cell communication & community behaviour
Polysaccharides & proteins – fundamental structural elements of biofilms, mechanical
strength
Lipids , nucleic acids – stability of biofilms
Extracellular DNA – required for initial biofilm establishment by P.aeruginosa
Composition of biofilms
6. Quorum sensing
Biofilm requires self organisation and co-operation among the cells.
Cell to cell signaling – Role in biofilm formation ,achieved by quorum sensing.
Cell density-dependent signaling system mediated by chemicals called autoinducer
molecules produced by bacteria during growth.
When the bacterial population reaches the quorum level ie.the signal concentration
reaches a threshold concentration sufficient to facilitate binding to the receptor.
Binding of the autoinducers is followed by activation or repression of target genes.
Quorum sensing allows bacteria to display a unified response that benefits the
population
AIs : oligopeptides – G+ bacteria ; N-Acetyl homoserine – G- bacteria
Boronated diester moleculles – inter species communication – both G+ , G- bacteria
Symbiosis, transfer of conjugative plasmids, sporulation, antimicrobial peptide
synthesis, regulation of virulence – mediated by quorum sensing.
9. Role of biofilms in antibiotic resistance
Delayed penetration of the antimicrobial agent
EPS – diffusional barrier ; delays rate of transport of drugs
Chemical action of drugs with EPS
Bacteria intact in biofilms more resistant than single cells
Altered growth rate of organisms in biofilms
organisms grow more slowly in biofilms
Slow uptake of antimicrobials
Actively growing and dividing cells are required
for drug action
10. Role of biofilms in disease production
Detachment of cells and cell aggregates : Bacteria detached from biofilm - role in
disease production in blood and urinary tract
G- bacteria in biofilms – produce endotoxins
Extracellular slime produced by S.epidemidis - interferes macrophage mediated
phagocytosis
Opsonizing antibodies – ineffective against bacteria in biofilms in CCF.
Antibodies produced by vaccination – ineffective when pathogen is encysted in
biofilms.
Biofilm resident bacteria – resistant to oxidative killing (E.coli)
Humans : biofilms play role in cystic fibrosis, otitis media, endocarditis,
periodontitis etc.
11. Role of biofilms in bovine respiratory disease
complex
Biofilms aid in resistance to antimicrobial drugs & evasion of host immune response
12. Role of biofilms in disease production
Leptospira sps – biofilm formers - new insights in pathogenesis
Leptospira interrogans – biofilm formation aid in long term survival in
aqueous environment
Biofilm formation and disease production - play an important role in
keeping the bacteria alive in the kidneys of animals such as rats without
causing disease.
13. Biofilms in medical devices
biofilms – frequent menace in urinary
catheters, contact lenses , prosthetic
heart valves , central venous catheters
biofilms grow well in lens care fluids.
ReNu lens care fluid used worldwide –
supports biofilms formed by the fungus
Fusarium sps.
Also formed in food substances,
vegetables
14. Biofilm examination & measurement
Differential interference contrast microscopy
Transmission electron microscopy
Scanning electron microscopy
Atomic force microscopy
Confocal laser scanning microscopy - FISH & 16S – 23S rRNA
hybridization
Roller tube method
Endoluminal brush biofilm measurement
Alginate brush method
BIOFILM INTERVENTION STRATEGIES
Prevent initial device contamination
Minimize initial microbial cell attachment to the device
Penetration of EPS matrix and cell killing
Removal of the device
17. Summary
Bacteria adopt biofilm as a success strategy to colonize and produce
disease.
Biofilm is the predominant mode of bacterial growth
Development of non invasive early biofilm detection methods will aid
in great success in bioilm treatment
Novel treatments should aim at distruption of quorum sensing and
inhibit the transcription of genes involved in biofilm formation.