Introduction
Bacterial infections constitute a significant risk to human and animal health, especially with the rise of antibiotic resistance (de Kraker et al., 2016). One possible alternative to antibiotics is bacteriophage (phage) therapy, which uses viruses that can infect and kill bacteria (Kortright et al., 2019). Phage therapy has been used for over a century but is not widely known or accepted in most parts of the world (Fauconnier, 2019). The project aims to improve the efficacy of phage therapy by testing different combinations of phages against Pseudomonas aeruginosa biofilms.
Methods
We used two methods to measure the effects of phage cocktails on biofilms: crystal violet staining and MTT assay ((3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide). The first method quantifies the biofilm biomass by staining the extracellular matrix and the bacterial cells, and the second method measures the biofilm activity by assessing the metabolic activity of the bacterial cells.
Results
The results show that phage cocktails with different numbers of phages in the formulation have different impacts on biofilm biomass and biofilm activity. Three critical points were observed in both parameters: a minimum number of phages required to initiate biofilm reduction, an optimal number of phages that achieved the maximum biofilm reduction, and a maximum number of phages that caused a plateau or a rebound effect on biofilm growth.
Conclusion
We conclude that phage cocktails with more than 20 phages in the formulation do not improve the efficacy of phage therapy against Pseudomonas aeruginosa biofilms. Moreover, they may have negative consequences such as reduced phage stability. Therefore, creating phage cocktails with unique compositions and dosages for each biofilm infection is required for optimal treatment.