## 3 Bacteriophage Depolymerases as an Alternative to Antibiotics
This feature greatly limits polysaccharides that can be digested by a particular depolymerase. In effect, a depolymerase originated from a particular phage may not recognize the cell-surface polysaccharide compounds of closely related bacteria or even those produced by bacteria of the same strain but growing under different conditions [105]. Furthermore, susceptibility of biofilms to phage depolymerases is dependent on the content of microorganisms and whether the biofilm is single- or multispecies. Importantly, polymicrobial systems not only are limited to different bacterial species, but may also encompass different genera and even other organisms, such as fungi. In comparison with single-species biofilms, the mixed communities are undoubtedly the dominant form in nature; however, they are more difficult to remove by phage depolymerases [52]. Furthermore, as reported by [PERSON] et al., bacteria in multispecies biofilms display higher resistance to other antibacterial agents than biofilms formed by these bacterial species alone [115]. One possible reason for this is the limitation of antibiotic agent migration by the presence of a large diversity of EPSs produced by heterogeneously distributed bacteria. In such a heterogeneous community, the action of depolymerases is limited due to the fact that they are highly specific for the host-derived polysaccharides [116]. Complex EPSs of multispecies biofilms may not only hinder the penetration of the biofilm by depolymerase-producing phages, but also entrap the phage in the biofilm matrix [117], reduce multiplication of the phage due to the presence of phage non-susceptible or metabolically inactive cells [118], reduce the presentation of the phage receptor [119], or deter the phage depolymerase activity [120]. In effect, pockets of unattainable phage-susceptible bacteria are formed, enhancing the structural heterogeneity of multispecies biofilms [116]. Importantly, there have been attempts to overcome the abovementioned difficulties in combating polymicrobial biofilm communities. One of them involves phage depolymerases, able to degrade EPSs of different bacterial species. As reported by [PERSON] et al., over a 90% reduction in dual-species biofilm was obtained using polysaccharide, isolated from a bacteriophage [121]. On the other hand, multispecies biofilms can also be treated with cocktails consisting of different phages/depolymerases acting on different receptors/structures, and this strategy is even recommended [122; 123] (for more examples, see review [116]). In addition, genetic modifications of phages could allow them to produce several depolymerases and extend their host range [99; 114]. They have been subjected to genetic engineering and purified [114]. Importantly, free recombinant enzymes are more easily produced than virion-associated depolymerases. Moreover, such recombinant enzymes may be applied at high concentrations, which overcome enzyme production by phages alone. Currently, work is underway to expand the spectrum of their activities [124]. In the fight against biofilms (including multispecies communities), depolymerases can also be used in combination therapy with antibiotics, phages, or other agents. Examples of such combination strategies are discussed in Section 4. _The Antibiofilm Activity of Phage Depolymerases: Examples of Applications of Phage Depolymerases against Bacterial Biofilms_  
EPSs are mainly responsible for the structural and functional integrity of bacterial biofilms and have an influence on their virulence [125]. Interestingly, [PERSON] et al. [126] applied the EPS depolymerase Dpo7, derived from bacteriophage vB_SepiS-philPLA7, against staphylococcal biofilms. This study revealed that Dpo7 is able to degrade the EPS biofilm matrix of staphylococcal strains from 31% in _S. epidermidis_ ASLD1 to 75% in _S. epidermidis_ LO5081, relative to the control variants.