## 2 Characterization of Bacterial Biofilms
### Alternative Strategies for Combating Bacterial biofilms
It is also speculated that the anti-attachment bacterial response to the presence of the polymer may be regulated by bacterial cell-to-cell communication through QS mechanisms [6; 12]. An alternative approach to combat bacterial biofilms is to reduce formation of persisters that are one of the main barriers for the effectiveness of antibiotic therapy. These dormant cells are protected by the biofilm matrix and have probably disabled their programmed cell death (PCD) to allow survival of a few cells if the antimicrobial agent reaches the whole population [29; 78]. Therefore, a novel anti-persister strategy is associated with the inhibition of the (p)ppGpp-regulated stringent response that is probably the main signal leading to dormant cell formation [32; 79]. It has also been shown that silver, halogenated indoles, and the 1018-peptide may increase antibiotic sensitivity and attenuate biofilm virulence [80; 81; 82]. Undoubtedly, all factors affecting persister cells are desirable because they decrease the multidrug tolerance of the biofilm. Antibiofilm strategies based on nanotechnology are also noteworthy. These methods include a wide range of metal-based nanoparticles (silver, gold, titanium, zinc, or copper), polymer-based nanoparticles, and green nanoparticles that are known for their antimicrobial action [30; 37; 83] It is well known that silver has been widely employed as an antimicrobial agent with a broad spectrum of activity against bacterial biofilms. The nanoparticles made of silver have been shown to interact with bacterial membrane proteins, intracellular proteins, and phosphate residues in DNA, as well as to interfere with cell division, leading to bacterial death [84]. The toxicity of silver nanoparticles is a serious problem that limits their use to certain sites. Oxidative stress, DNA damage, and cytokine induction have been proposed as three main mechanisms responsible for cytotoxic effects [85]. Disinfection methods are also able to disrupt the biofilm. They are based on the cleaning of medical and industrial equipment by using chemical alkali-based and acid-based agents, ethanol, chlorine dioxide, or hydrogen peroxide, coupled with physical methods, such as scrubbing and flushing [15]. Importantly, the activity of phages against biofilm is also exploited. This strategy is based on single phages or phage cocktails, phage-derived enzymes, phages in combination with antibiotics, and genetically modified phages [33; 86; 87]. Although phages depend upon a metabolically active bacterial host to replicate, and they are generally unable to replicate in dormant/persister cells until these are reactivated, one might suggest an advantage of using these viruses against biofilms due to their lytic activity against bacteria with reduced (although not completely inhibited) metabolism. Moreover, although most phages can be affected by the EPS matrix, they remain able to disseminate within the biofilm and replicate, at least to some extent. Importantly, bacteriophages are not motile agents, and they should preferably be added directly to the biofilm. They present high specificity against bacterial species and even strains. Furthermore, the development of bacteriophage resistance is another concern that arises in the case of phage therapy [88]. The use of monoclonal antibodies (mAbs) is an another interesting antibiofilm strategy. [PERSON] et al. presented human mAbs that could bind the bacterial amyloid curli and inhibit curli monomer polymerization, thus disrupting biofilm formed by _S. enterica_ serovar Typhimurium. Biofilm treated in this way displayed changes in ECM composition and a \"loose\" structure. Moreover, injection of the human mAbs facilitated the antibiotic-mediated eradication of biofilms formed on a glass slide and vascular catheter [89]. As indicated previously, antibody-based approaches can be used to combat biofilms of various bacterial species, such as _S. aureus_, _A. baumannii_[90], or _S. epidermidis_[91].