, L. casei is a fastidious microorganism ( Cai et al., 2009 and Du Toit et al., 2011) and the pool of free amino acids and peptides in milk is not sufficient to fulfill optimal bacterial growth. Thus, the phage-induced release of the S. thermophilus cell lysate, which contains proteases, lactase, free amino acids, and peptides, accelerates the growth and propagation of the probiotic.