## 3 Bacteriophage Depolymerases as an Alternative to Antibiotics
Additionally, the pre-treatment of polystyrene surfaces with Dpo7 resulted in the reduction of biofilm activity and its biomass from 53% to 85% in the majority (67%) of tested strains (the obtained results were dose-dependent and time-independent). In summary, EPS depolymerase Dpo7 may inhibit biofilm formation and can also disperse biofilms generated by different strains of _S. epidermidis_ and _S. aureus_[126]. Moreover, [PERSON] et al. [127] isolated a novel bacteriophage Petty that possesses the gene of depolymerase Dpo1 (capable of degrading EPSs) and can infect _A. nosocomial_s and _A. baumannii_. The main purpose of that study was to determine the ability of Dpo1 to depolymerize EPSs and to remove bacterial biofilm formed by _Acineto-bacter_ strains. In vitro analyses showed that Dpo1 was able to reduce EPS viscosity and to remove biofilms of some of the tested _Acineto-bacter_ strains. However, the antibiofilm effect of Dpo1 was not spectacular, and it led to a 20% reduction of the bacterial biofilm. The obtained results may suggest that the phage depolymerase Dpo1 cannot completely destroy bacterial biofilms. On the other hand, Dpo1 may probably decrease the virulence of the tested bacterial strains via the degradation of EPSs [127]. In another research, [PERSON] et al. [128] investigated the efficacy of newly isolated phage IME180 against biofilms formed by _P. aeruginosa_. This lytic phage possesses a gene that encodes a functionally active depolymerase. Surprisingly, this phage-derived enzyme is able not only to inhibit the formation of host bacterial biofilms, but also to reduce the biomass of a preformed biofilm. However, complete inhibition of biofilm formation or its removal was not observed [128]. It is worth mentioning that the ability to form biofilm is also observed in the group of _E. coli_ bacteria [129]. [PERSON] et al. [130] isolated and characterized phage vB_EcoM_ECOO78 that infects clinical isolates of _E. coli_. This phage belongs to the _Myoviridae_ family, and it encodes a functionally active depolymerase Dpo42. Researchers have demonstrated that Dpo42 may degrade the capsular polysaccharides surrounding _E. coli_ cells. Moreover, this enzyme can also exhibit antibiofilm activity in a dose-dependent manner. The highest level of antibiofilm activity was observed when Dpo42 was added to a final concentration of 25 ug/well. However, it was also shown that the depolymerase Dpo42 can significantly prevent biofilm formation, but cannot remove it totally [130]. In subsequent studies, depolymerase Dep6 (O91-specific polysaccharide depolymerase) was identified in the lytic T7-like phage, named PHB19, specific for Shiga toxin-producing _E. coli_ (STEC). Dep6 was tested for antibiofilm and antibacterial activities against _E. coli_ strains. Application of the Dep6 enzyme significantly reduced the absorbance of the total 24 h old and 48 h old biofilm biomasses, compared to untreated controls. However, Dep6 did not decrease the number of counted viable bacterial cells. Interestingly, this depolymerase may probably degrade EPS on the surface of the STEC HB10 strain, thus enhancing the susceptibility of this strain to serum killing [54]. _K. pneumoniae_ has also demonstrated resistance to a wide range of antibiotics. This pathogen also belongs to the group of bacteria that are able to form biofilms [131]. Interestingly, depolymerase Dep42 was identified in lytic bacteriophage SH-KP152226 that represents the _Podoviridae_ family and can lead to the lysis of _K. pneumoniae_ capsular type K47 [132]. Treatment with 10 ug/mL Dep42 resulted in a reduction in bacterial counts in the biofilm, compared to the control. [PERSON] et al. [132] also demonstrated that EPSs from _K. pneumoniae_ strain 2226 can be degraded by Dep42. These results showed that depolymerase Dep42 weakly reduced the number of colonies in the biofilm but had the ability to degrade the extracellular material of the biofilm, releasing the attached cells.