Current and Emergent Control Strategies for Medical Biofilms - Antibiofilm Agents: From Diagnosis to Treatment and Prevention - page 132

concentrations of the oils attenuated biofilm formation by S. aureus and
S. epidermidis strains on polystyrene microtiter plates. Agarwal et al. ( 2008 ) stud-
ied 30 plant oils for their activity against C. albicans biofilms. Peppermint, euca-
lyptus, ginger grass, and clove oils resulted in a reduction in C. albicans biofilm
formation. Dalleau et al. ( 2008 ) performed a study on 10 terpenic derivatives,
corresponding to major components of essential oils, for their activity against
C. albicans biofilms. Almost all the studied terpenic derivatives showed antibiofilm
activity; however, carvacrol, geraniol, and thymol exhibited the strongest activity.
Moreover, these compounds also proved to be efficient against biofilms made by
C. glabrata and C. parapsilosis . In addition, Hendry et al. ( 2009 ) have shown potent
antibiofilm activity from the main component of eucalyptus oil, 1,8-cineole, against
C. albicans biofilms.
Harjai et al. ( 2010 ) reported anti-QS activity by fresh Allium sativum extract
[fresh garlic extract (FGE)] and subsequently inhibited P. aeruginosa biofilm
formation by 6 log10 units. Moreover, in vivo prophylactic treatment in a mouse
model of kidney infection with FGE (35 mg/mL) for 14 days resulted in a 3 log10
unit decrease in the bacterial load on the fifth day after infection compared to
untreated animals. They found that FGE also protected renal tissue from bacterial
adherence and resulted in a milder inflammatory response and histopathological
changes in infected tissues. FGE inhibited expression of P. aeruginosa virulence
factors such as pyoverdin, hemolysin, and phospholipase C. Moreover, killing
efficacy and phagocytic uptake of bacteria by peritoneal macrophages was
enhanced by administration of garlic extract.
Issac Abraham et al. ( 2011 ) reported efficacy of Capparis spinosa (caper bush)
extract to inhibit biofilm formation by 73 %, at a concentration of 2 mg/mL, in
E. coli . Also, for the pathogens Serratia marcescens , P. aeruginosa, and
P. mirabilis , biofilm biomass was reduced by 79, 75, and 70 %, respectively.
Moreover, the mature biofilm structure was disrupted for all of the studied patho-
gens. Furthermore, the addition of C. spinosa extract (100 g/mL) to a bacterial

culture resulted in swimming and swarming inhibition. Similarly, Melia dubia
(bead tree) bark extracts were examined by Ravichandiran et al. ( 2012 )ata
concentration of 30 mg/mL. In their study, these extracts reduced E. coli biofilm
formation by 84 % and inhibited expression of virulence factors, such as hemoly-
sins, by 20 %. Bacterial swarming regulated by QS was inhibited by 75 %, resulting
in decreased biofilm expansion. Recently, our group (Khan and Ahmad 2012a , b )
has shown antibiofilm activity by Cymbopogon citratus and Syzygium aromaticum
essential oils and active compounds, namely cinnamaldehyde and eugenol, in drug-
resistant strains of C. albicans (Fig. 4 ).

μ

Interference with Quorum Sensing

A new drug target is to interfere with the process of QS, a phenomenon of
communication cross talk. This phenomenon is used by many pathogenic microor-
ganisms to establish a biofilm and control much of their virulence arsenal.