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Molecular Microbiology Research (Online) 2013, Vol.3 No.1 1-8
ISSN 1027-5595
http://mmr.sophiapublisher.com
4
substance. But in the latter case, this trait was resilient
when there was addition of carbohydrate source in the
growth medium. Manifestation of the slime-associated
antigen appeared to be species specific characteristic
and limited to the
S. epidermidis
isolates. Its strong
relationship with the ability to produce intense biofilm
contents showed slime-associated antigen as a
possible virulence indicator for
S. epidermidis
.
Transmission and scanning electron microscopes were
used by Christens
e
n et al.
(1982) for the detection of
slime production by
S. epidermidis
. The results of this
study showed that slime producing strains were
enclosed in an adhesive layer on the catheter surface.
Perversely, the non-slime producers were not enclosed.
It was concluded that slime associated attachment may
be a perilous feature in the pathogenesis of
S.
epidermidis
infections associated with implantation of
medical devices (e.g. prosthetic cardiac valves,
cerebrospinal fluid shunts, orthopedic appliances and
intravascular catheters).
4 Biofilm and Disease Production
It has been shown by direct observation of bacteria in
natural settings that they usually grow adhered to
surface-liquid or liquid- air interfaces and embedded
in a self-produced extracellular polymeric matrix
(Costerton et al., 1999). It is suggested that firstly the
bacteria attached to the surface of ducts and alveoli in
the mammary glands and start production of toxins.
These attached bacteria enhance macrophage
instigation and neutrophils movement from the blood
into the milk (resulting in an increase in the somatic
cell count), mammary gland swelling, host defense
impairment and the epithelial cell damage. The
bacteria will reach the basal sub-epithelial cell layers,
fix fibrinogen along with other host receptor proteins
and establish the infection that eventually becomes
chronic (Foster and Hook, 1998).
Mostly long-lasting infections are associated with
bacterial growth in the form of adhesive colonies
surrounded by a large exopolysaccharide matrix,
creating a biofilm (Costerton et al., 1999). Biofilms
are resistant to macrophage mediated phagocytosis
due to their aggregate size and also become resistant
to some antibiotics (Monzon et al., 2002). The
extracellular matrix has complex structure that varies
between different bacterial species and even within
the same species in different environmental circum-
stances (Maira-Litran et al., 2004).
Regardless of their heterogeneous composition,
exopolysaccharides are important component of
biofilm matrix and provide the framework for
microbial cells to be inserted into it (Branda et al.,
2005). The most common exopolysaccharides are
cellulose and β-1,6 linked N-acetylglucosamine. They
are the most common components of the biofilm
matrix of many different bacteria. In addition to
exopolysaccharides, exterior proteins also play an
essential role in biofilm formation. Many of the
external proteins intricate in biofilm production have
several mechanical and practical features in common
and therefore, the existence of a group of external
proteins has been proposed. Biofilm associated protein
(Bap) was explained in a
S. aureus
bovine mastitis
isolate as the first member of this group (Lasa and
Penades, 2006).
Maturation of biofilm provides further protection to
bacterial cells due to production of another slime layer,
glycocalyx. The chemical structure of these slime
films is still unknown but evidence suggested that it is
principally composed of hydrated polysaccharides.
The nutrient supply inside the biofilm becomes
limited which results in decreased growth potential of
the bacterial biofilms and discrete drift through
channels across the biofilm aim to preserve profusion
(Stoodley et al., 2002). Some other dynamics like
oxygen profusion, carbon source, osmolarity and
internal pH control the biofilm maturation. When the
biofilm attained a serious mass, a vibrant stability is
reached then the outer most layers begin to produce
free living organisms. These bacteria are free to sneak
away the biofilm and to inhabit other surfaces (Dunne,
2002).
5 Biofilm and Antibiotic Resistance
The bacteria carrying this typical peculiarity are
highly resilient to antibiotics. This type of resilience
can involve different reasons including (a) exopoly-
saccharides (EPS) produced by the biofilm producing
organisms which provide them physical/ chemical