2.3. Designing the optimal multiplicity of infection

The optimal multiplicity of infection (MOI) is the ratio of phages to bacteria at the time of infection. The experimental method followed was according to the study mentioned in the reference (Sun et al., 2022). In brief, the CFU/ml of the host cell at the exponential growth phase was counted through the dilution coating method with serial dilutions of 10⁻⁴, 10⁻⁵, and 10⁻⁶. Phage stock of known titer and host cells at the exponential stage were mixed with a gradient of MOI ranging from 0.001 to 10 and cultured in a shaker (180 rpm/min) at 28°C for 12 h. The enrichment was centrifuged at 15,000 × g at 4°C for 15 min and filtered through a 0.22-μm filter membrane, and the phage titer was determined by the double-layer agar plate method with three replicates.