Current and Emergent Control Strategies for Medical Biofilms - Antibiofilm Agents: From Diagnosis to Treatment and Prevention - page 141

P. aeruginosa and Agrobacterium tumefaciens (Geske et al. 2005 ). They also
demonstrated that two of their most active synthetic AHLs could retard biofilm
formation in P. aeruginosa PA01. Other research that includes the modification of
AHLs to discern their effects on QS and biofilm formation in P. aeruginosa comes
from the Suga group. The work exploited the synthesis of a 96-member library
constructed through solid phase protocols to mimic AHLs by replacing the
homoserine lactone moiety with a variety of functionalities. A noteworthy com-
pound identified within this study was AHL derivative 8, which had no effect on
biofilm growth, yet elicited a noticeable change in the biofilm morphology of
P. aeruginosa PA01 (Smith et al. 2003a , b ). Analogues of P. aeruginosa AHLs in
which the lactone functionality was replaced by a ketone had additional
difluorination between the

-keto amide positions (Glansdorp et al. 2004 ).
Junker and Clardy ( 2007 ) have developed a HTS method for small molecule
inhibitor of P. aeruginosa biofilms at the Institute of Chemistry and Cell Biology-
Longwood (ICCB-L) at Harvard Medical School, Boston, MA ( http://iccb.med.
harvard.edu/ ). They have obtained 66,095 compounds, from natural products of
microbial or plant origin and also some commercial chemical compounds, to
identify those that prevent biofilm formation without affecting planktonic bacterial
growth. The screen is a luminescence-based attachment assay that has been vali-
dated with several strains of P. aeruginosa and compared to a well-established but
low-throughput crystal violet staining biofilm assay. They have determined the
potencies of 61 compounds against biofilm attachment and have identified 30 com-
pounds that fall into different structural classes as biofilm attachment inhibitors
with 50 % effective concentrations of less than 20

ʲ

M. The most active compound
discovered was shown to possess an IC50 value of 530 nM for biofilm inhibition.
This makes this compound as one of the most active biofilm modulators ever
disclosed against either Gram-positive or Gram-negative bacteria. Their study has
highlighted these small-molecule inhibitors for identification of their relevant
biofilm targets or potential therapeutics for P. aeruginosa infections.
A structure-based virtual screen (SB-VS) for the identification of putative QS
inhibitors was carried out using a focused database comprising compounds that
possess structural similarities to the known QS inhibitors furanone C30, patulin, the
P. aeruginosa LasR natural ligand (3-oxo-C12-AHL 5), and a known QS receptor
agonist TP-1, (Yang et al. 2009 ). This screen led to the discovery of three com-
pounds, which were all recognized drugs, salicylic acid, nifuroxazide, and
chlorzoxazone, and were subsequently shown to significantly inhibit
QS-regulated gene expression at concentrations at which they did not affect bacte-
rial growth. In addition to affecting QS regulated virulence factor production, these
compounds were shown to affect biofilm formation by PA01. Screening of approx-
imately 66,000 compounds and natural product extracts from the Center for Chem-
ical Genomics at the University of Michigan to identify compounds that affected
induction of a V. cholerae c-di-GMP-inducible transcriptional fusion led to the
discovery of a novel benzimidazole (Sambanthamoorthy et al. 2011 ). This com-
pound was examined for its ability to inhibit biofilm formation by a number of
pathogenic bacterial strains. Compound 61 was shown to be a broad spectrum

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