Phage Adsorption to Lactococcal Cells

Adsorption of phage to host cells was performed as described (Madera et al., 2003 (link)). Phage c2 was added at a MOI of 0.001 to stationary-phase host cultures diluted to an OD₆₀₀ of 0.8 in GM17 supplemented with 10 mM of Ca(NO₃)₂ and 10 mM MgSO₄. Following a 10 min incubation at room temperature, the phage-host mixture was centrifuged for 5 min, and phage counts in the supernatant determined by standard double-layer agar assays. A sample without cells was equally treated to determine the initial phage titer. The percentage adsorption was calculated as (1-residual phage titer/initial phage titer) × 100. Experiments were carried out with two to five independent lactococcal cultures.