Biomedical Engineering Reference
In-Depth Information
S. epidermidis , has the ability to produce intracellular adhesion mediated by
the ica locus. This data suggests that the early stages in biofilm formation
may be similar for the two organisms (Cramton et al. 1999). Enterococci
are important pathogens in device-related infections and, like other Gram-
positive organisms, the formation of enterococcal biofilms on medical implants
is increasingly becoming an important clinical issue (Shay et al. 1995).
In similarity to Gram-negative organisms, Gram-positive bacterial cells
also produce extracellular polysaccharides (often referred to as “slime”) when
growing on a surface. Deighton and Borland showed that S. epidermidis
increased slime production in iron-limited medium and later in the growth
phase when nutrients were exhausted. They suggested that this observation
may be an important signal in vivo , when iron nutrient levels may be limit-
ing (Deighton and Borland 1993). S. aureus also produces EPS or slime in a
phase-variable manner. The increased EPS correlates to its capability to form
a biofilm in an in vitro system (Baselga et al. 1993).
There is no much data on the potential detachment of Staphylococci or
Enterococci from their biofilms as well as on the control of this process. Expres-
sion of the ica locus may be phase variable, as Ziebuhr and colleagues (1999)
proposed that the “switch-off” of ica by the IS256 insertion element may
be the mechanism by which individual S. epidermidis (and possibly also S.
aureus ) cells can leave the biofilm and colonize on new surfaces.
4.3.2 Fungal Biofilms
Fungal infections are abundant especially in immunocompromised patients
and in patients treated with high doses of antibiotics, and are a growing con-
cern. It has been recognized that, like bacteria, fungi and yeast, for example,
Candida albicans, are also capable of biofilm formation on medical implants
(Kojic and Darouiche 2004; Hawser and Islam 2006). Hawser and Douglas
reported the use of disks made of catheter material as a simple assay for
biofilm development in vitro (Hawser and Douglas 1994; Hawser and Islam
2006). Using this system, they showed that C. albicans could form biofilms on
a wide range of abiotic surfaces and that biofilm formation occurred best on
latex, poly(vinylchloride), or silicone elastomer, but less on polyurethane or
pure latex (Hawser and Douglas 1994). Baillie and Douglas (1999) went on to
use this model system in a series of elegant experiments to show that switching
between yeast form and hyphal growth form plays an important role in fun-
gal biofilm development. Using scanning electron microscopy as their research
tool, they observed that the biofilm layer closest to the surface was primarily
composed of yeast cells, while the upper portion of the biofilm was composed
of a layer of hyphae. Baillie and Douglas (1999) also showed that the surface
to which the yeast cells attached could influence the structure of the biofilm
formed and that the structure of the fungal biofilms formed resembled their
bacterial counterparts.
The fungal biofilm developed, however, new physiological properties that
were different from their planktonic counterparts. Douglas and colleagues used
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