Data were analyzed by normality tests ( Shapiro - Wilk and Kolmogorov - Smirnov ): a normal distribution was confirmed . Thus , in comparison of the irradiation conditions and CFU counts , data were analyzed with a parametric test ( Dunnett 's or Tukey test ) by SPSS v15.0 ( IBM , Armonk , NY , USA ) , with significance accepted at p < 0.05 .