Biomedical Implications of the Porosity of Microbial Biofilms - Porous Media: Applications in Biological Systems and Biotechnology - page 131

The complexity of signals triggering biofilm development is evident from
the fact that organisms have multiple genetic pathways that control this
behavior. In P. fluorescens , multiple pathways control biofilm formation
and function under different growth conditions (Hinsa and O'Toole 2006).
V. cholerae may have at least three different means for adhering to surfaces
depending on whether this organism is within its human host or in an aqueous
environment (Zampini et al. 2005), while E. coli K-12 can form biofilms on
abiotic surfaces under a wide range of environmental conditions (Beloin et al.
2008).
Following attachment to a surface, bacteria undergo further adaptation
to life as biofilm. Two properties are often associated with this phenomenon:
enhanced biosynthesis of EPS (Beloin et al. 2008) and the development of
antibiotic resistance (Mah and O'Toole 2001). These features appear to create
a protective environment, converting the biofilms to a tenacious clinical prob-
lem. Bacterial biofilms may also develop other properties, including increased
resistance to UV light, increased rates of genetic exchange, altered biodegrada-
tive capabilities, and increased secondary metabolite production (Goodman
et al. 1994; Brazil et al. 1995; Moller et al. 1998).
Detachment and return to the planktonic growth mode is an important
portion of the biofilm development pathway. Boyd and Chakrabarty (1994)
reported that the enzyme alginate lyase may play a role in the detachment
phase in P. aeruginosa . Allison and colleagues (1998) showed that a biofilm of
P. fluorescens decreased in size following an extended incubation, attributed,
at least in part, to loss of EPS.

4.3.1.2 Biofilms Composed of Gram-Positive Bacteria

A number of Gram-positive bacterial infections, caused by S. epidermidis ,
S. aureus, and the Enterococci , have proved to be particularly dicult to
eradicate with currently available antibiotic therapies, in part due to their
high-level natural resistance to antimicrobial compounds. Furthermore, these
organisms become resistant to the highest doses allowed for antibiotics when
growing in a biofilm (Raad et al. 1995).
The initiation of the attachment event has proven to be a critical stage
in biofilm development. Mutants of S. epidermidis , which could be isolated
with a microtiter dish-based assay, were not able to form biofilms on abi-
otic surfaces (Heilmann and Gotz 1998), a capability that is strongly corre-
lated to the initiation of diseases under clinical settings (Deighton and Balkau
1990). Genetic studies have also led to the conclusion that biofilm development
by this organism occurs initially via cell-surface interaction (Heilmann and
Gotz 1998). These interactions may be mediated through a number of factors,
including uncharacterized surface proteins (Hussain et al. 1997), extracellular
proteins (Schumacher-Perdreau et al. 1994), capsular polysaccharide/adhesion
(PS/A) (McKenney et al. 1998), and the cell surface-localized autolysin
(Heilmann et al. 1997). Cramton and colleagues showed that S. aureus , like