Role of quorum sensing in bacterial infections

Table 1 Quorum sensing systems and quorum sensing-virulence associated phenotypes in the reviewed organisms

Organism	QS systems	Regulated phenotypes
Gram (-) bacteria
Pseudomonas aeruginosa	(1) LasI (S)-LasR (R)-HSL (s)	Expression of several virulence factors including: Pyocyanin, pyoverdine, elastase, alkaline protease, HCN, rhamnolipids and biofilm formation
	(2) HSL RhlI-RhlR
	(3) Alkyl quinolones (PQS)
Vibrio harveyi	(1) LuxM (S)-LuxN (R)- 3OHC4HSL (s)	Expression of bioluminescence genes and several virulence factors including: Siderophores, protease, EPS production
	(2) LuxS (S)-LuxP (R)-AI-2 (s)
	(3) CqsA (S)-CqsS (R)-CAI-1 (s)
Vibrio cholerae	(1) LuxS (S)-LuxP (R)-AI-2 (s) (2) CqsA (S)-CqsS (R)-CAI-1 (s)	Expression of several virulence factors including: Biofilm formation and EPS production.
Vibrio fischeri	(1) LuxI (S)-LuxR (R)-3OC6HSL (s)	Expression of bioluminescence, host colonization and motility genes
	(2) AinS (S)-AinR (R)-C8HSL (s)
	(3) LuxS (S)-LuxP (R)-AI-2 (s)
Acinetobacter spp	(1) Abal (S)-AbaR (R)-3OHC12HSL (s)	Expression of virulence factors including biofilm formation.
Burkhordelia cepacea	(1) Cep1 (S)-CepR (R)-C8HSL,C6HSL (s)	Expression of swarm motility genes and several virulence factors including: proteases, siderophores, toxins, antifungal agents and biofilm formation
	(2) Ccil (S)-CciR (R)-C8HSL,C6HSL (s)
Escherichia coliSalmonella typhimurium	(1) Unknown (S)-SdiA (R)-3OC8HSL (s) (2) LuxS (S)-LsrB (R)-AI-2 (s) (3) Unknown (S)-QseC (R)-AI-3 (s)	Expression of motility genes, acid resistance and virulence factors including biofilm formation
Gram (+) bacteria
Staphylococcus aureus	(1)AgrB (S)-AgrC (R)-AIP(s)	Expression of several virulence factors including: hemolysins, leukocidins, cell surface adhesins, exoenzymes, and biofilm formation
Fungi
Candida albicans	2-phenylethanol, tryptophol, farnesol, farnesoic acid, and tyrosol as (s)	Fungal dimorphism, biofilm formation and expression of virulence genes
Mucor rouxii, Histoplasmacapsulatum, Ceratocystis ulmi	QS (s) unknown	Fungal dimorphism
Saccharomyces cerevisiae	Phenylethanol and tryptophol as (s)	Transition from yeast to filamentous form
Protozoa
Trypanosoma cruzi	SIF soluble factor as (s)	Differentiation of replicating to non-dividing forms
Mammal cells
CD4+T cells	IL-2 (s) and IL-2Rα (R)	Regulation of the CD4+T cells population
Cancer cells	Multiple (S) and (R) and paracrine factors as (s)	Regulation of the metastatic process

IL-2: Interleukin 2; SIF: Soluble inhibitory factor; QS: Quorum sensing; PQS: Pseudomonas quinolone signal; EPS: Exopolysaccharide.