*2.3.4 Metal chelators*

Removal of metals from the microbial environment via metal chelators renders bacteria more susceptible to antimicrobial agents, as metals are essential for different cellular processes [108]. Ethylenediaminetetraacetic acid (EDTA), the most-known metal chelator, has been reported to exhibit antibiofilm activity against *S. aureus*, and to eradicate the *in vivo* biofilm models on catheters [109]. Combination of EDTA with minocycline has effectively reduced the colonization of *S. epidermidis*, *S. aureus* and *C. albicans* on catheters [110]. Similarly, the combination of EDTA and fluconazole remarkably inhibited biofilm assembly in *C. albicans* [111].

#### *2.3.5 Enzymes*

Based on their target, the antibiofilm enzymes are classified into three types: polysaccharide-degrading enzymes, nucleases and proteases.

### *2.3.5.1 Polysaccharide-degrading enzymes*

Alpha amylase enzyme was found to inhibit biofilm formation by *S. aureus* through the detachment of biofilm and interfering with aggregation of cells [112]. Dispersion B, a bacterial glycoside hydrolase, degrades poly-N-acetylglucosamine (PNAG), a main matrix exopolysaccharide of *S. aureus* and *E. coli* [113]. Such polysaccharide is produced by many bacteria and fungi and plays an important role in surface adhesion, and biofilm formation. Furthermore, PNAG was reported to successfully disrupt the biofilm matrix of *S. epidermidis* [114]. Moreover, the combination of dispersion B and triclosan was reported to significantly reduce biofilm formation of *E. coli*, *S. aureus* and *S. epidermidis* [115].

**199**

*New Approaches for Competing Microbial Resistance and Virulence*

Deoxyribonuclease I (DNase I) degrades DNA in biofilm matrix [104]. Moreover, it was shown to have antibiofilm activity and to detach the biofilms produced by different bacterial species [116]. Such nuclease can prevent the initial adherence of microbial cells to surfaces via the degradation of cell surface-associated nucleic acids that act as surface adhesins [117]. Furthermore, DNase I has been found to increase the sensitivity of bacterial cells in biofilm matrix to antibiotics,

Proteases act as antibiofilm agents because they are able to inhibit cell-cell communication, in biofilms, via hydrolysis of extracellular protein fibers and surface adhesins [104]. Subtilisins, a class of serine proteases produced by Bacillus species, were reported to prevent the adherence of microorganisms to surfaces [119]. The coating of silicone surfaces with multiple layers of amylase or acylase has been found to inhibit biofilm formation in case of *P. aeruginosa* and *S. aureus* [120]. Another example is lysostaphin, a metalloprotease produced by *Staphylococcus simulans*, was shown to prevent the adherence of *S. aureus* to lysostaphin-coated

d-Amino acids have been shown to inhibit biofilm formation in *B. subtilis*, via activating the release of amyloid fibers [122]. Such inhibitory effect was reversed by their cognate l-amino acids [123]. Furthermore, d-amino acids were shown to have

Exogenous generation of nitric oxide (NO) by agents, for example, sodium nitroprusside has been shown to trigger the bacterial growth from the biofilm form to the planktonic form via the reduction of the level of cyclic di-GMP inside the bacterial cells [104]. Further NO-generators, for example, S-nitroso-N-acetyl penicillamine and S-nitroso-l-glutathione were found also to induce the dispersion of *P. aeruginosa* biofilm [124]. The dispersion of biofilm by NO-generators was also demonstrated in *B. subtilis* [125]. Recently, it has been reported that catheters charged with NO prevented the adherence and the colonization of *P. aeruginosa*, *E.* 

Alkaloids are a group of natural organic compounds that contain a nitrogen atom and are present in different species of plants. The alkaloid berberine has been reported to inhibit biofilm formation in *S. epidermidis* biofilm at a concentration of 30 μg/mL, possibly via binding to the amyloid proteins in the biofilm matrix [127]. Reserpine has been shown to effectively prevent biofilm formation in *K. pneumoniae* at a concentration of 0.0156 mg/mL, which was 64-fold lower than its minimum inhibitory concentration [128]. Tetrandrine inhibited biofilm formation of *C. albicans* at a concentration of 32 mg/L, which is the MIC50 of that

antibiofilm activity in case of *P. aeruginosa* and *S. aureus* [122].

*DOI: http://dx.doi.org/10.5772/intechopen.90388*

resulting in reduction of biofilm mass [118].

*2.3.5.2 Nucleases enzymes*

*2.3.5.3 Proteases*

catheters [121].

*2.3.6 Amino acids*

*2.3.7 Nitric oxide generators*

*2.3.8 Natural agents*

*coli* and *C. albicans* on their surfaces [126].

alkaloid against *C. albicans* SC5314 [129].
