Current and Emergent Control Strategies for Medical Biofilms - Antibiofilm Agents: From Diagnosis to Treatment and Prevention - page 120

the incidence of biofilm-related infections. Studies have reported the use of several
compounds and synthetic analogues to prevent biofilm formation such as farnesol,
quaternary ammonium salts, and silver ions, which were shown to effectively
inhibit both bacterial and fungal biofilm formation (Gottenbos et al. 2001 ; Hashi-
moto 2001 ; Jabra-Rizk et al. 2006 ; Shirtliff et al. 2009 ). One particular study
highlighted the role of two quaternary ammonium silanes (QAS) to coat silicone
rubber tracheoesophageal shunt prostheses, yielding a positively charged surface.
One QAS coating [(trimethoxysilyl)-propyldimethyloctadecylammonium chloride]
was applied through chemical bonding, while the other coating, Biocidal ZF, was
sprayed onto the silicone rubber surface. This was the first report on the inhibitory
effects of positively charged coatings of tracheoesophageal shunt prostheses on the
viability of yeasts and bacteria in mixed biofilms (Oosterhof et al. 2006 ). Although
the study initially aimed at reducing voice prosthetic biofilms, its relevance extends
to all biomedical surfaces where mixed biofilms develop and become problematic.
Similarly, dental resin material coated with thin-film polymer formulations
containing the polyene antifungal nystatin, AMB, or the antiseptic agent chlorhex-
idine were used in C. albicans and mixed biofilm prevention (Redding et al. 2009 ).
The polysaccharide dextran is widely used in medicine and is also one of the
main components of dental plaque. Cross-linked dextran disks soaked with AMB
solutions, described as amphogel, killed fungi within 2 h of contact and could be
reused for almost 2 months without losing their efficacy against C. albicans
(Zumbuehl et al. 2007 ). This antifungal material is biocompatible and could be
used to coat medical devices to prevent microbial attachment.
Another option is to coat biomaterial surfaces with organic molecules to prevent
protein adsorption which may also inhibit biofilm formation (Njoroge and
Sperandio 2009 ). Coating of medical material surfaces has been employed and
tested with several types of coating molecules, including the naturally occurring
polymer chitosan and antimicrobial peptides such as Histatin 5 (Hst5). Histatins, a
family of histidine-rich cationic peptides, are secreted by the major salivary glands
in humans, especially histatin 5, which possess significant antifungal properties. A
recent study demonstrated that histatin 5 exhibited antifungal activity against
C. albicans biofilms and to a lesser extent against C. glabrata biofilms developed
on denture acrylic (Konopka et al. 2010 ).
Naturally occurring antimicrobial peptides are promising therapeutic agents
against pathogens such as C. albicans . But they are difficult and expensive to
produce in large quantities and are also often sensitive to protease digestion.
Therefore, their development as coating agents has been hampered. The search
for new and improved antimicrobial peptides has led to the study of peptide
mimetics. Synthetic analogs that mimic the properties of these peptides have
many advantages and exhibit potent and selective antimicrobial activity (Tew
et al. 2002 ). New classes of antimicrobial peptides were designed to mimic trans-
membrane segments of integral membrane proteins and were tagged with lysine
residues to facilitate solubilization in aqueous media. These peptides, designated
kaxins, have a non-amphipathic hydrophobic core segment, which distinguishes
them from many natural linear cationic antimicrobial peptides. With this peptide