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One of the things that makes bacteriophages genuinely exciting as a therapeutic tool is the same thing that makes them scientifically interesting to study. They are specific.
A phage does not wander around infecting every bacterium it encounters. It has a range. A set of bacterial species or strains that it can infect, and everything outside that range it simply ignores. This is called host range, and understanding it is one of the most important steps in moving from finding a phage to potentially using one.
Think of it like a key. A phage has surface proteins that need to fit specific receptors on a bacterial cell wall to get inside. If the receptor is not there, the door does not open.
Today, at The Technical University of Kenya, Nairobi, Cohort 003 moved into the plaque assay step, working from the serial dilutions they ran on the positive samples identified earlier in the week. Using the Double Layer Agar (DLA) method, they were able to get results, count individual plaques, calculate phage titre, and describe the morphology of what they were seeing. Each plaque is the physical signature of a phage doing its work. Counting them and describing them carefully is how you begin to understand what you are actually dealing with.
They also practiced plaque picking, lifting individual plaques from the DLA plates. What follows from here is a cycle of repetition: serial dilution, spot assay, plaque assay, again and again, typically three to five rounds, until what you have is a pure phage and not a mixture. The picking today was the first step of that process.
Our appreciation goes to Jonathan Mutinda and James Munyao King PhD for guiding the participants with the practicals.