Quorum Sensing

1.4 Biofilms and
Biofilm Dispersion

Adhesion to and growth on surfaces as biofilms is a common feature

of bacteria and other microorganisms in their natural environments

[41]. Growth as surface-adherent biofilm communities confers sig-

nificant antimicrobial protection to microorganisms, which in some

cases can approach values of 1000-fold reduced susceptibility in

comparison to planktonic values [42]. Unlike traditional resistance

mechanisms which tend to persist regardless of growth mode, the

reduced susceptibility of biofilm bacteria to antibiotics is classified as

Fig. 3C. violaceumpigmentation inhibition assay is used to detect QS disruption

inC. violaceum12472 ((11) as modified [33]). Here, AHLs or enzymes that

disrupt the binding of theC. violaceumcognate AHL (C6 HSL) cause a loss of

pigmentation in the vicinity of the test organism in the center of the plate. In (a)

(positive control),P. aeruginosaPAO1 AHLs (C4-HSL, and 3-o-C12 HSL) interfere

with theC. violaceumCviR receptor. Pigmentation inhibition is absent (negative

control, (b)) in the vicinity of C6-HSL-producingC. violaceumstrain 31532,

although the 31532 strain itself is nonpigmented. (c) shows the pigmentation

inhibition, due to an uncharacterized quorum-disrupting compound produced by

an environmental isolate [58] (RJC McLean and C Fuqua, unpublished). (d)

shows a plate in which a potential quorum-inhibiting compound has been placed

into a well in the center of the plate andC. violaceum12474 spread across the

plate. Growth inhibition is seen close to the quorum inhibitor, and quorum

inhibition (arrow) is indicated by the nonpigmented zone. More details are

given in the text

Bioassays of Quorum and Biofilm Dispersion Signals 9