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Biofilms

Biofilms. Dense aggregates of surface-adherant microorganisms embedded in an exopolysaccharide matrix. 65% of human bacterial infections involve biofilms!. Streptoccus spp. S. mutans – ubiquitous in oral microflora. Ecologic niche: Biofilms can lead to dental caries

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Biofilms

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  1. Biofilms • Dense aggregates of surface-adherant microorganisms embedded in an exopolysaccharide matrix. • 65% of human bacterial infections involve biofilms!

  2. Streptoccus spp. • S. mutans – ubiquitous in oral microflora. • Ecologic niche: • Biofilms can lead to dental caries • Acid tolerant response • Natural genetic competence • Bacteriocin activity

  3. DENTAL CARIES – demineralization of the tooth by bacteria. http://www.db.od.mah.se/car/data/cariesser.html

  4. Quorum sensing • Cell-cell communication. • Production, detection, and response to autoinducers (extracellular signaling molecules). • Bacteria can monitor population density and coordinate gene expression.

  5. Quorum sensing • Involved in regulation of biofilms, virulence, antimicrobial production, bioluminescence, etc. • Gram positive and gram negative bacteria. • Inter- and intra-specific communication!

  6. Henke and Bassler, 2004. Three parallel quorum-sensing systems regulate gene expression in Vibrio harveyi. Journal of Bacteriology 186: 6902-6914.

  7. Biofilms • Facilitate horizontal gene transfer? • S. mutans biofilm transformation frequences 10-600 x that of planktonic cells. • Subpopulations in biofilms constantly competent for DNA uptake compared to 15-30 min. transient state in planktonic cells.

  8. Dental biofilms • Oral environment stressors: • Nutrient shortage and excess • Low pH • High osmolarity • Oxidation • Host ingestion of antimicrobial agents. Genetic transformation for antimicrobial resistance or virulence factors may provide important selective advantages to bacteria in these environments.

  9. Acid Tolerance Response ATR experiments: • Exposure to pH 5.0-6.0 allows the bacteria to adapt and survive at 3.0-3.5. • Filtrates from acid-adapted cells induced an ATR in cells not exposed to low pH. • Bacteria grown at high density adapted faster than cells grown at low density. • S. mutans biofilms more resistant to low pH and even grew at the low pH after a glucose pulse in contrast to planktonic cells.

  10. Biofilm survival advantage • High population density. • High concentration of signal molecules. • Heterogenous adaptation possible. • Bacteria sensing stress can signal more distant bacteria to adapt!

  11. Mucosal pathogens • Bacterial concentrations are often lower on mucosal surfaces than in dental plaque due to bathing effects of secretions and desquamation. • Quorum sensing still important: • S. pneumoniae quorum sensing mutant was less virulent than parent strain in mouse model.

  12. Bacteriocins • Antimicrobial peptides generated by bacteria that target other bacteria. • Quorum sensing pathways involved: • S. pyogenes has parts of quorum sensing apparatus but not CSP to enhance DNA uptake. • A specialized niche to regulate bacteriocin activities in a cell density dependent manner to outcompete other bacteria on mucosal surfaces, but not involving DNA uptake? Other signals?

  13. http://cgi.darwinawards.com/cgi/frames.pl?/book/3chapter05.htmlhttp://cgi.darwinawards.com/cgi/frames.pl?/book/3chapter05.html

  14. -Squid-bacteria symbiosis involving quorum sensing, trickery, and a daily love-hate relationship!

  15. Symbiosis Strategy The players: • Euprymna scolopes – a Hawaiian squid • Vibrio fischeri – bioluminescent bacteria

  16. Timing is everything… • At birth – squid light organ has no bacteria. • Within hours – symbiotic colonization. • Each morning – >90% of bacteria expelled from squid light organ. • Each night – bacteria multiply in squid light organ and bioluminesce for squid camouflage.

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