Bacterial biofilms represent a complex and dynamic system in which bacterial cells are interconnected with each other and attached to a surface, embedded within a matrix of extracellular polymeric substances (EPS). Biofilm growth represents the predominant form of microbial life on Earth and a key survival strategy of bacteria, characterized by reduced metabolic activity, altered gene expression and protein synthesis, as well as increased EPS production. Due to this multilayered defense system, biofilms exhibit remarkable resistance to physical, chemical, and biological factors, making their removal a major challenge in both clinical and industrial environments. Limited efficiency of chemical approaches and the increasing number of antibiotic-resistant bacteria have recently directed growing attention toward alternative strategies. Among the most promising are lytic bacteriophages—viruses that specifically infect bacterial cells and destroy them in the final stage of their lytic cycle.
In the experimental part of this study, we established a continuous system consisting of a stirred (chemostat) and tubular bioreactor under defined conditions (constant temperature, pressure, linear velocity, dilution rate, and physiological state of the bacteria) to investigate the formation, stability, and removal of Staphylococcus epidermidis and Staphylococcus capitis biofilms. The results showed that S. epidermidis formed a more compact, homogeneously distributed, and stable biofilm compared to S. capitis, which exhibited weaker cell adhesion and higher cell release in the outlet section during the rinsing phase. Lytic bacteriophages (phage COP-80B for S. epidermidis and phage Kayvirus kay for S. capitis) effectively lysed planktonic bacteria but showed no activity against preformed biofilms, regardless of their age or the medium used for phage delivery. The experimental findings thus confirm the high resistance of biofilms and the limitations of using bacteriophages as a standalone approach for their removal. At the same time, we also demonstrated key limitations of the colony‑forming unit method for determining bacterial concentration, as the presence of non-cultivable cells and cellular aggregates leads to an underestimation of the actual size of the biofilm population.
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