**2. Biofilm formation in** *S. epidermidis*

*S. epidermidis* infections are regarded as prototypic biofilm infections. The process of biofilm formation by *S. epidermidis* is periodically dynamic. Also, surface adhesion between planktonic bacterial cells is a key for biofilm formation. Once several cells succeed in adhering on a surface, named initial attachment of cells, surface motility and binary division result in an aggregation of attached cells. These primary cell aggregates produce exopolymers, including exopolysaccharides and extracellular proteins, which form extracellular matrix. Some of those factors may also originate from lysed cells, such as extracellular DNA (eDNA) [10]. Subsequently, there is development of a multicellular, multilayered biofilm architecture. In the later phase of biofilm formation, biofilm cells and clusters can detach. This detachment process is of key importance for the dissemination of biofilm-associated infection [10].

### **2.1 Factors involved in primary attachment in** *S. epidermidis* **biofilm formation**

Nonspecific adhesions between bacterial cells, which are mainly attributed to the composition of compounds on the surface of bacterial cells and their hydrophobicities, play an important role in biofilm formation. Additionally, autolysin (AtlE) and teichoic acids have influences on biofilm formation [11, 12]. It is reported that lots of autolysin enhanced the cell surface hydrophobicity and increased the biofilm formation. Also, teichoic acids correlated with increased cell surface hydrophobicity, so they contributed to biofilm formation [11, 12].

In vivo primary attachment occurs to host tissue or host matrix proteins. *S. epidermidis* produces a variety of surface proteins binding host proteins in a specific manner. Bacterial surface proteins with such capacities have been termed microbial components recognizing adhesive matrix molecules (MCRAMM) [13]. The C-terminus of such bacterial surface proteins consists of an LPxTG (Leu-Prox-Thr-Gly) motif containing Gram-positive cell wall anchor, which covalently links to the cell wall [1]. According to genomic analyses, *S. epidermidis* has at least 14 MCRAMMs with an LPxTG motif. Many of those belong to the serine-aspartate (SD)-repeat-containing protein family (called Sdr). The SD-repeat region spans the cell wall and extends the ligand-binding region from the surface of the bacteria [14]. Adequate SD repeats within proteins are essential for outstanding from bacterial cell surface, which are covalently anchored to the peptidoglycan of Grampositive bacteria.

The SD repeat family protein Sdr G in *S. epidermidis,* which is very similar to a fibrinogen-binding protein (Fbe), is necessary and sufficient for binding to fibrinogen-coated material. SdrG knock-out mutant showed less adhesion on fibrinogen-coated surfaces. It is reported that in vivo anti-SdrG antibody decreased the numbers of *S. epidermidis* cells adherent to biomaterials [14]. One of Sdr proteins, SdrF, mediates binding to type I collagen via one or both ɑ1 chains, named collagen-binding protein [15].

Some of surface proteins on bacterial cell wall are adherent to host cells via noncovalent interaction, such as hydrophobic bonds and Van der Waals' force, which of

**103**

the same strains [20].

*Formation, Antibiotic Resistance, and Control Strategies of* Staphylococcus epidermidis *Biofilm*

process are involved into the polymers on bacterial cell surface, e.g., teichoic acids. Teichoic acids are main components consisting of the cell wall of Gram-positive. They bind to peptidoglycan of cell wall and influence the activity of autolysin (AtlE). AtlE, encoded by the atlE gene, is a bifunctional autolysin: one is able to mediate bacterial adhesion, and the other is to promote bacterial cell autolysis, which releases DNA out of cells, named extracellular DNA (eDNA) [16].

**2.2 Factors responsible for cellular aggregation in** *S. epidermidis* **biofilm** 

*S. epidermidis* [18]. *S. epidermidis* ATCC 35984 is a ica+

**2.3 Biofilm formation and maturation**

Following the primary attachment of cells to a surface, bacterial cells occur to accumulate with the help of a variety of associated-accumulation factors, such as polysaccharide intercellular adhesin (PIA), accumulation-associated protein (Aap),

In the process of biofilm formation by *S. epidermidis*, PIA plays an important role in cell aggregation. Studies with *S. epidermidis* mutant revealed that the accumulation-defective mutants were unable to form a biofilm as they were unable to display intercellular aggregation or to produce PIA [17]. Further characterization of this *S. epidermidis* mutant showed that a deletion of icaR gene was found to upregulate PIA expression, providing evidence that this gene negatively regulates the PIA expression [17]. However, it is reported that there is no ica operon in some of clinical *S. epidermidis* strains, which have capacity of biofilm formation, named ica or PIAindependent type. In these strains, the accumulation-associated protein (Aap) is a major factor contributing to exopolysaccharide-independent biofilms of *S. epidermidis* [1]. Aap protein promotes cell-cell adhesion via a Zn2+-dependent mechanism [18]. It is reported that 90% of isolated *S. epidermidis* strains contain aap gene, which is implicated in both PIA-dependent and PIA-independent biofilm formations of

whose biofilm formation mainly depends on PIA consisting of reducing polysaccharides in which dihydroxyl groups are unsubstituted. However, exopolysaccharides in

Cellular aggregation constantly occurs and subsequently forms biofilm. Disruptive molecules create channels in the biofilm, which are essential for nutrient accessibility in deeper biofilm layers and give the biofilm its characteristic structure, often described as mushroom-like shapes [10]. The characteristic structure of mature biofilms with mushroom-like shapes and channels is dependent on the

**3. Mechanisms of antibiotic resistance in** *S. epidermidis* **biofilms**

Several in vitro studies have demonstrated that bacteria within biofilms are more resistant against antibiotic treatment as compared to planktonic cultures of

Of primary importance for dissemination of biofilm-associated infection, cells or cell aggregates may detach from a mature biofilm to reach the next infection sites. This may occur by mechanical forces under flow, such as present in a blood vessel, in a process often called sloughing [10]. Additionally, the bacteria can trigger detachment by PSM production. These surfactant-like molecules work by decreas-

ica<sup>−</sup> *S. epidermidis* mainly consist of nonreducing polysaccharides [19].

production of phenolsoluble modulins (PSMs) in *S. epidermidis*.

ing noncovalent adhesion between bacterial cells.

strain and a biofilm former,

*DOI: http://dx.doi.org/10.5772/intechopen.89800*

**formation**

and so on.

*Formation, Antibiotic Resistance, and Control Strategies of* Staphylococcus epidermidis *Biofilm DOI: http://dx.doi.org/10.5772/intechopen.89800*

process are involved into the polymers on bacterial cell surface, e.g., teichoic acids. Teichoic acids are main components consisting of the cell wall of Gram-positive. They bind to peptidoglycan of cell wall and influence the activity of autolysin (AtlE). AtlE, encoded by the atlE gene, is a bifunctional autolysin: one is able to mediate bacterial adhesion, and the other is to promote bacterial cell autolysis, which releases DNA out of cells, named extracellular DNA (eDNA) [16].

### **2.2 Factors responsible for cellular aggregation in** *S. epidermidis* **biofilm formation**

Following the primary attachment of cells to a surface, bacterial cells occur to accumulate with the help of a variety of associated-accumulation factors, such as polysaccharide intercellular adhesin (PIA), accumulation-associated protein (Aap), and so on.

In the process of biofilm formation by *S. epidermidis*, PIA plays an important role in cell aggregation. Studies with *S. epidermidis* mutant revealed that the accumulation-defective mutants were unable to form a biofilm as they were unable to display intercellular aggregation or to produce PIA [17]. Further characterization of this *S. epidermidis* mutant showed that a deletion of icaR gene was found to upregulate PIA expression, providing evidence that this gene negatively regulates the PIA expression [17]. However, it is reported that there is no ica operon in some of clinical *S. epidermidis* strains, which have capacity of biofilm formation, named ica or PIAindependent type. In these strains, the accumulation-associated protein (Aap) is a major factor contributing to exopolysaccharide-independent biofilms of *S. epidermidis* [1]. Aap protein promotes cell-cell adhesion via a Zn2+-dependent mechanism [18]. It is reported that 90% of isolated *S. epidermidis* strains contain aap gene, which is implicated in both PIA-dependent and PIA-independent biofilm formations of *S. epidermidis* [18]. *S. epidermidis* ATCC 35984 is a ica+ strain and a biofilm former, whose biofilm formation mainly depends on PIA consisting of reducing polysaccharides in which dihydroxyl groups are unsubstituted. However, exopolysaccharides in ica<sup>−</sup> *S. epidermidis* mainly consist of nonreducing polysaccharides [19].

### **2.3 Biofilm formation and maturation**

Cellular aggregation constantly occurs and subsequently forms biofilm. Disruptive molecules create channels in the biofilm, which are essential for nutrient accessibility in deeper biofilm layers and give the biofilm its characteristic structure, often described as mushroom-like shapes [10]. The characteristic structure of mature biofilms with mushroom-like shapes and channels is dependent on the production of phenolsoluble modulins (PSMs) in *S. epidermidis*.

Of primary importance for dissemination of biofilm-associated infection, cells or cell aggregates may detach from a mature biofilm to reach the next infection sites. This may occur by mechanical forces under flow, such as present in a blood vessel, in a process often called sloughing [10]. Additionally, the bacteria can trigger detachment by PSM production. These surfactant-like molecules work by decreasing noncovalent adhesion between bacterial cells.

### **3. Mechanisms of antibiotic resistance in** *S. epidermidis* **biofilms**

Several in vitro studies have demonstrated that bacteria within biofilms are more resistant against antibiotic treatment as compared to planktonic cultures of the same strains [20].

*Bacterial Biofilms*

*Pseudomonas aeruginosa* [6–9].

biofilm-associated infection [10].

ity, so they contributed to biofilm formation [11, 12].

**2. Biofilm formation in** *S. epidermidis*

agents [4, 5]. Moreover, some Actinomycete species were reported to produce inhibitors against biofilm formation by *Staphylococcus aureus*, *Escherichia coli*, and

formation of *S. epidermidis* and review the control strategies to biofilm.

With this background, we aim to present the current knowledge on biofilm

*S. epidermidis* infections are regarded as prototypic biofilm infections. The process of biofilm formation by *S. epidermidis* is periodically dynamic. Also, surface adhesion between planktonic bacterial cells is a key for biofilm formation. Once several cells succeed in adhering on a surface, named initial attachment of cells, surface motility and binary division result in an aggregation of attached cells. These primary cell aggregates produce exopolymers, including exopolysaccharides and extracellular proteins, which form extracellular matrix. Some of those factors may also originate from lysed cells, such as extracellular DNA (eDNA) [10]. Subsequently, there is development of a multicellular, multilayered biofilm architecture. In the later phase of biofilm formation, biofilm cells and clusters can detach. This detachment process is of key importance for the dissemination of

**2.1 Factors involved in primary attachment in** *S. epidermidis* **biofilm formation**

Nonspecific adhesions between bacterial cells, which are mainly attributed to the composition of compounds on the surface of bacterial cells and their hydrophobicities, play an important role in biofilm formation. Additionally, autolysin (AtlE) and teichoic acids have influences on biofilm formation [11, 12]. It is reported that lots of autolysin enhanced the cell surface hydrophobicity and increased the biofilm formation. Also, teichoic acids correlated with increased cell surface hydrophobic-

In vivo primary attachment occurs to host tissue or host matrix proteins. *S. epidermidis* produces a variety of surface proteins binding host proteins in a specific manner. Bacterial surface proteins with such capacities have been termed microbial components recognizing adhesive matrix molecules (MCRAMM) [13]. The C-terminus of such bacterial surface proteins consists of an LPxTG (Leu-Prox-Thr-Gly) motif containing Gram-positive cell wall anchor, which covalently links to the cell wall [1]. According to genomic analyses, *S. epidermidis* has at least 14 MCRAMMs with an LPxTG motif. Many of those belong to the serine-aspartate (SD)-repeat-containing protein family (called Sdr). The SD-repeat region spans the cell wall and extends the ligand-binding region from the surface of the bacteria [14]. Adequate SD repeats within proteins are essential for outstanding from bacterial cell surface, which are covalently anchored to the peptidoglycan of Gram-

The SD repeat family protein Sdr G in *S. epidermidis,* which is very similar to a fibrinogen-binding protein (Fbe), is necessary and sufficient for binding to fibrinogen-coated material. SdrG knock-out mutant showed less adhesion on fibrinogen-coated surfaces. It is reported that in vivo anti-SdrG antibody decreased

proteins, SdrF, mediates binding to type I collagen via one or both ɑ1 chains, named

Some of surface proteins on bacterial cell wall are adherent to host cells via noncovalent interaction, such as hydrophobic bonds and Van der Waals' force, which of

the numbers of *S. epidermidis* cells adherent to biomaterials [14]. One of Sdr

**102**

positive bacteria.

collagen-binding protein [15].

### *Bacterial Biofilms*

*S. epidermidis* and other bacterial species produce an extracellular matrix called glycocalyx or slime, which is a highly hydrated complex composed of teichoic acids, proteins, and exopolysaccharides. In biofilms, poor antibiotic penetration, nutrient limitation and slow growth, and formation of persister cells are hypothesized to be responsible for drug resistance.
