title: Cell density--dependent regulation: basic principles and effects on the virulence of Gram-positive cocci.
abstract: BACKGROUND
  Quorum sensing (QS) regulation appears to be a consequence of interbacterial communication by which bacteria of one or even different species learn about their current population density and react in a defined way to that information. QS-regulation is a three step process: in the first step specific signaling molecules are produced and secreted to the exterior space. In the second step, the molecules accumulate e.g. with growing population density. In the last step, a supra-threshold concentration of the molecules is extra- or intra-cellularly sensed by the bacteria and leads to a cascade of regulatory activities. While Gram-negative bacteria can employ five or more different chemical classes of signaling molecules, Gram-positive cocci predominantly use special oligopeptides for specific signaling.
  
  
  METHODS
  Examples of QS-regulatory effects on virulence factor expression in Staphylococcus aureus, Streptococcus mutans, and Enterococcus faecalis are given. In these bacteria, QS-regulation appears to be crucial for displaying tissue invasiveness and/or biofilm formation.
  
  
  CONCLUSIONS
  The high specificity of the initial signal sensing and the importance for expressing special virulence traits make this type of gene expression control a promising target for the development of novel therapeutics. The options for such therapies are critically discussed based on practical experiences with interference in S. aureus QS-regulation.
authors.affiliation: Department of Medical Microbiology & Hospital Hygiene, University Hospital, Schillingallee 70, D-18057, Rostock, Germany. andreas.podbielski@med.uni-rostock.de
authors.forename: Andreas
authors.initials: A
authors.lastname: Podbielski
authors.forename: Bernd
authors.initials: B
authors.lastname: Kreikemeyer
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000502:physiology; D013293:Enterococcus faecalis / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D016908:Gram-Positive Bacterial Infections / Q000382:microbiology*; D006095:Gram-Positive Cocci / Q000235:genetics / Q000472:pathogenicity* / Q000502:physiology; D006801:Humans; D008954:Models, Biological; D009842:Oligopeptides / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D013211:Staphylococcus aureus / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology; D013295:Streptococcus mutans / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology; D015534:Trans-Activators / Q000502:physiology; D014157:Transcription Factors / Q000502:physiology; D014774:Virulence / Q000235:genetics / Q000502:physiology; D037521:Virulence Factors
chemical_list: D001426:Bacterial Proteins; D009842:Oligopeptides; D015534:Trans-Activators; D014157:Transcription Factors; D037521:Virulence Factors