Some strains of yeasts can develop killer phenotype derived from cytoplasmic dsRNA in a VLP in which viral toxin protein is secreted to kill sensitive yeasts of the same species. We aimed to investigate various commercial and clinical probiotic strains of S. boulardii reaction under the influence of killer toxin strains (K1 and K2), thus killer strains and no-killer strains were used as controls. Moreover, the linked gene CNVs among the strains for killer sensitivity can be determined and studied further.