Biomedical Engineering Reference
In-Depth Information
Poloxamer hydrogel, being liquid at low temperatures and solid at cultivation temperatures,
has been proposed (Percival et al., 2007) as a culture support in the Petri dish to induce
bacteria and yeast biofilm-like aggregates. The thermoreversible gelation makes the
preparation and the recovery of biofilm samples easy and reproducible but still requires
further confirmation for use in biofilm biology. Powder material, such as titanium powder,
provides increasing support surfaces that are similar to cell culture on beads; moreover, it
allows the anchored phase to be easily separated from the planktonic phase by simple
sedimentation (Ahariz & Courtois, 2010). The titanium surface is not antimicrobial by itself,
so it can be used as support for
Candida
biofilm. Titanium is widely employed for implant
manufacturing due to its good biocompatibility and mechanical properties, but infection
remains as a primary cause for failure, leading to removal.
Candida albicans
biofilms on
titanium powder could offer a simple and reliable model for further investigation of new
antimicrobial strategies; moreover, the model could be extendable to other microorganisms
contaminating implanted materials. Making implant surfaces resistant to microbial
colonization should reduce infectious complications; however, such developments need an
in vitro
model that allows the effect of surface modification and coatings on biofilm
production to be studied. This aspect will be detailed in the next section.
The approach by means of static cultures simplifies the
in vivo
complexity to interactions
between one single species and one single support without considering the numerous
salivary compounds and abundant oral microflora in the real oral environment.
Microorganisms in biofilms
in vivo
display properties different from those observed under
laboratory conditions. The single-species procedures can be extended to a two-membered
microbial co-culture or a characterized microbial consortium in order to reconstitute a
medium for approaching oral microcosm and containing sterilized or artificial saliva. Multi-
species biofilms have already been investigated on various dental materials such as enamel,
amalgam, composite, and acrylic to assess the role of surface roughness (foremost in the first
steps of biofilm formation) and impact of (pre)conditioning by saliva (Dezelic et al., 2009).
Diffusion of drugs through biofilms, including
Candida
biofilms, can be documented by an
experimental perfusion system superposing disk, filters, biofilm, and agar containing the
drug under evaluation (Samaranayake et al., 2005). Perfusion of drugs in biofilms allows the
putative factors that lead to biofilm antimycotic resistance to be evaluated.
3.1.2 Continuous culture models
Contrary to static cultures, continuous culture models (flow cells, Modified Robbins Device,
chemostats, artificial mouths, and constant depth film fermenter) take into account oral flow
and oral bathing conditions as shear forces and nutrient supplies (Bernhardt et al., 1999;
Ramage et al., 2008). Indeed, oral biofilms on prosthetic materials are exposed to salivary
fluxes conveying water and nutrients to the aggregated microorganisms in the saliva. For
instance, liquid flow has been shown to influence the production of an extracellular matrix
by
Candida albicans
biofilms
in vitro
(Hawser et al., 1998). Taking extracellular material
produced in static cultures as a basal value, a gentle stirring significantly multiplied this by
~1.25, while a more intense stirring led to complete inhibition. Other data (Biswas &
Chaffin, 2005) reported the absence of
Candida albicans
biofilm formation in anaerobiosis
even if this yeast can grow in anaerobic environment. Yeast retention against a continuous
flow of medium has been used as a marker for yeast adhesion to a surface in the same
manner as the retention after liquid washes (Cannon et al., 2010). Cultures under continuous
flow conditions facilitated the penetration of
Candida
albicans
into silicone elastomers when
