This study aimed to modify Staphylococcus aureus by using physical and chemical mutagens and subjections the cell wall to the hydrolytic activity of lysozyme. Chemical mutagenesis by N-methyle-N-nitro-N-nitroguanidine, was achieved by incubating the cell suspension of Staphylococcus aureus with 100μg/ml MNNG for different periods of time (5, 10, 15, 20, 25 and 30min).Aliquot of 100μl of the bacterial suspension subjected to the lethal and mutagenic effect of MNNG, then spread on BHI agar and incubated at 37°C over night in dark. After incubation, 180 colonies were randomly selected and screened for their ability to grow on the same medium supplemented with 3.4 and 12.5μg/ml lysozyme to detect the lysozyme sensitive mutants. Results showed that all of the selected colonies were able to grow on 12.5μg/ml lysozyme containing medium except one colony (S1). Physical mutagenesis by UV radiation was achieved by subjecting cell suspension of S. aureus to different doses of UV radiation (1, 2, 3, 4 and 5J/m2).Aliquot of 100μl of the bacterial suspension was exposed to the lethal and mutagenic effect of UV radiation then spread on BHI agar and incubated at 37°C over night in dark. After incubation, 160 colonies were randomly selected and screened for their ability to grow on the same medium but containing 3.4 and 12.5μg/ml lysozyme. Results showed that all of the selected colonies were able to grow on these media except four colonies (S2, S3, S4, and S5) which were unable to grow on 12.5μg/ml lysozyme containing medium, these four colonies were considered to be lysozyme sensitive mutants.
