Biofilms & Polymicrobial Infections III

• What is quorum sensing?

  The regulation of gene expression in response to fluctuations in cell-population density
• What do microbes secrete?

  Quorum sensing molecules (QSM)
• What do QSMs do?


  When present in sufficient concentrations, they induce the expression or repression of quorum-dependent target genes- changes in transcriptional activity

  
  

  Specific changes in population behaviour occur when a critical threshold of signalling is exceeded
• What are some examples of bacterial QSMs?

  
• Is quorum-sensing just restricted to bacteria?

  No, fungi can do it too

  
• What is farnesol?

  A QSM that inhibitsCandida albicansfilamentation

  
• What is important for biofilm persistence?


  Acquisition of nutrients
• What substrates are available in the oral cavity?

  Proteins, sugar, & glycoproteins
• What is the purpose of digestive consortiums?

  In general, individual microbial species are unable to completely degrade all these substrates on their own, however species can cooperate with each other to do so through the formation of digestive consortiums
• How does a digestive consortium work?

  
• What does polymicrobial cooperation allow microbes to do?


  To persist as part of a polymicrobial community in harsh environments that would otherwise be lethal to them in mono-culture
• How is polymicrobial cooperation achieved?

  Accessory pathogens:commensal microbes that can support or enhance the virulence of a different organism.

  
  

  An example of this is the dental abscess, as most oral bacteria are unable to form abscesses on their own, you need a minimum combination of 6-8 species

  
• What is another example of polymicrobial cooperation?

  The microbial subversion/evasion of host immune responses

  
• Describe the complexity of polymicrobial infections.

  A single periodontal pocket can have over 100 different bacterial species

  
  

  Unculturables are unable to grow as a single species without helper strains

  
• Is it easy to diagnose a polymicrobial infection?

  No, it's time-consuming and costly

  
  

  Organisms are present in varying levels so it'd be difficult to detect those in smaller numbers (keystone pathogens)

  
  

  You need 16S rRNA next-generation sequencing & OTU determination to identify the genus of the microbes

  
  

  And it's difficult identifying the organisms to a species level
• Is treatment of polymicrobial infection easy?

  No, it's really difficult because of the diversity of the species so it's difficult to choose an individual antimicrobial since not all organisms may respond
• What are the conclusions drawn from this lecture?

  
• Virulence

  degree of pathogenicity