# Biology and Regulation of Staphylococcusococcal Biofilm
## 2 Molecular Control of _S. aureus_ Biofilm Development and the Role of _ica_  
The formation of mature, three-dimensional biofilms is a complex process composed of different phases: attachment, accumulation, maturation, and dispersal [54; 55]. While the initial binding to abiotic (protein-free) surfaces in vitro is mostly based on hydrophobic interactions, primary attachment during infection occurs via the binding of specific bacterial surface receptors that recognize host matrix proteins [56]. This group of cell-wall-anchored proteins, named MSCRAMMs (for microbial surface components recognizing adhesive matrix molecules) [57; 58], presents a conserved structure containing 4-5 domains with the binding domain exposed to the extracellular medium. The accumulation phase appears to be related to the production of polysaccharide adhesins that allow interactions between  
Figure 1: Biofilm formation of _S. aureus_ (pCtwt-gfp) on glass slides coated with different biomaterials. (**A**) Confocal scanning laser micrographs of _S. aureus_ (pCtwt-gfp) biofilm formation on glass slides coated with titanium, cobalt–chromium, and amorphous Teflon. (**B**) Three-dimensional view of the fluorescence emitted by _S. aureus_ (pCtwt-gfp) in the biofilm. (**C**) Scanning electron micrographs (SEM) of the corresponding biofilms. _S. aureus_ adheres very strongly to surfaces coated with titanium and cobalt–chromium, yielding thick biofilms, while adherence to Teflon was decreased and a less-dense biofilm was formed (modified according [21]). bacterial cells [42; 59]. Thus, the primary determinant of the accumulation phase of staphylococcal biofilm formation relates on the production of the polysaccharide intercellular adhesin (PIA), a process that is dependent on the expression of genes of the _icaADBC_ operon [60; 61]. Biochemical studies have demonstrated that the PIA consists of polymeric \(N\)-acetylglucosamine in which the cells are embedded and protected against humoral and cellular host immune defense and against antibiotic treatments [14; 62; 63]. PIAs act as an intercellular adhesin, allowing for the integration of bacterial DNA [64] and constituting a stable, organized structure. They appear to play a role in the formation of multiple bacterial clusters that are involved in biofilm maturation and include the accumulation-associated protein [42; 65] and other proteins, such as clumping factor A (ClfA) [42], the staphylococcal surface protein (SSP1), and the biofilm-associated protein (Bap) [42]. With the increasing number of sequenced genomes due to progress in high-throughput sequencing capacity, an _ica_ locus has been identified in several staphylococci species: _S. caprae_, _S. roterodami_, _S. carnosus_, _S. saprophyticus_, _S. colmini_, _S. capitis_, _S. sciuri_, _S. hominis_, and _S. simulans_. It appears to serve the same function as in _S. aureus_. Note that if _S. aureus_ remains a potent human pathogen, most of these species represent potential human opportunistic pathogens. The _ica_ operon was first identified in _S. epidermidis_[39; 40] and has been studied most extensively in that species. The _ica_ operon is subject to environmental regulation [66]. For example, anaerobic growth was found to induce expression of the _ica_ operon and PIA production in both _S. epidermidis_ and _S. aureus_[46]. Expression of the _icaADBC_ operon appears tightly controlled in _S. aureus_, evidenced by the fact that it is expressed at very low levels under in vitro growth conditions [67]. [PERSON] et al. found that the mutation of _ica_ and the resultant inability to produce PIA had little impact on in vitro biofilm formation or the colonization of an abiotic surface [44]. Our group also compared an _S. aureus_ strain and its corresponding _ica_ mutant in a tissue cage model of infection and demonstrated that the _ica_ mutant retained the capacity to colonize at a similar level to the wild-type strain [68], a result which was confirmed by others [69].