Basic information about biofilms in microbiology

1. BIOFILMS
I.Sophia
Roll no: P-1699
VBM

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.

3. Biofilm formation

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.

8. Significance of biofilms

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

16. Coating indwelling devices with bactericidals, biocides, anti-adhesion compounds

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.