Bacterial Adhesion and Interaction with Biomaterial Surfaces - Biointerfaces: Where Material Meets Biology - page 370

the detachment of cell clusters from a biofilm. Biofilm maturation and
detachment processes are of key importance for the formation of vital
biofilms in vivo with the capacity of bacterial dissemination to secondary
sites of infection. 75
It is well accepted that the bacteria growing within a biofilm are unique
from those growing in the planktonic phase. Microarray studies have dem-
onstrated the differential gene expression profiling of staphylococci culti-
vated under biofilm and planktonic conditions. 76 As the cells grow in
biofilm, they also have the spatial and temporal responses to the immediate
environment, e.g., availability of nutrients and oxygen, resulted in the shift
of physiology toward to anaerobic or microaerobic metabolism and cell wall,
DNA synthesis. 26 Rani et al. demonstrated that staphylococcal biofilms
contain cells in at least four distinct states: growing aerobically, growing
fermentatively, dormant, and dead. The variety of activity states represented
in a biofilm may contribute to the special ecology and tolerance to anti-
microbial agents of biofilms. 77
Although the molecular mechanisms for the adhesion/accumulation of
staphylococcal cells to material surfaces have been investigated in great
detail, little is known for the forces and molecular determinants behind the
structuring of biofilms and the detachment of cellular clusters from bio-
films. Molecular proteins and polysaccharides are involved in biofilm mat-
uration. PIA is one of the most important adhesive biofilm molecules. 61,78
The growing list of biofilm adhesive proteins comprises accumulation as-
sociated protein (Aap), 70 extracellular matrix binding protein (Embp), 46
protein A, 79 Fg-binding protein 80 and others. Other polymers are also im-
plicated in staphylococcal biofilm formation. For example, teichoic acids
contribute to S. aureus biofilm formation 81 and eDNA is an essential part of
the network. 82 The agr (accessory gene regulator) quorum-sensing system
has been recognized to govern biofilm maturation. 83,84
As a biofilm matures, individual cells or intact section of biofilm can
detach and metastasize to other sites. It is important for the dissemination
of infection from surface of an indwelling medical device to other sites via
the lymph and blood stream. 75 Because staphylococcal biofilms are em-
bedded in an extracellular matrix composed of proteins, polysaccharides,
eDNA and other host factors, degradation of these matrix components can
disrupt established biofilms or prevent the biofilm formation. The pro-
duction of compounds such as proteases, 85 DNases, 86,87 and surfactants 88
that can degrade and solubilize adhesive components in biofilm matrix is
the primary mechanism of biofilm dispersal and detachment. 89 Recent work
demonstrated that phenol-soluble modulins (PSMs), a-helical peptides with
surfactant properties, secreted by S. epidermidis, promote biofilm structuring
and detachment in vitro and dissemination from colonized catheters in a
mouse model of device-related infection. 90 PSMs are regulated by the agr
quorum-sensing system, and all PSMs have been identified in S. aureus and
S. epidermidis, and known to participate in biofilm structuring and detach-
ment processes. 91-93

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