In most bacteria, a global level of regulation, termed quorum sensing (QS), 
exists involving intercellular communication via the production and response to 
cell density-dependent signal molecules. QS has been associated with a number of 
important features in bacteria including virulence regulation and biofilm 
formation. Consequently, there is considerable interest in understanding, 
detecting, and inhibiting QS. N-acylated homoserine lactones (AHLs) are used as 
extracellular QS signals by a variety of Gram-negative bacteria. Chromobacterium 
violaceum, commonly found in soil and water, produces the characteristic purple 
pigment violacein, regulated by AHL-mediated QS. Based on this readily observed 
pigmentation phenotype, C. violaceum strains can be used to detect various 
aspects of AHL-mediated QS activity. In another commonly used bioassay organism, 
Agrobacterium tumefaciens, QS can be detected by the use of a reporter gene such 
as lacZ. Here, we describe several commonly used approaches incorporating C. 
violaceum and A. tumefaciens that can be used to detect AHL and QS inhibitors. 
Due to the inherent low susceptibility of biofilm bacteria to antimicrobial 
agents, biofilm dispersion, whereby bacteria reenter the planktonic community, 
is another increasingly important area of research. At least one signal, 
distinct from traditional QS, has been identified and there are a variety of 
other environmental factors that also trigger dispersion. We describe a 
microtiter-based experimental strategy whereby potential biofilm dispersion 
compounds can be screened.