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SECTION I: MOLECULAR GENETIC ENGINEERING AND BIOCHEMICAL TECHNOLOGY 199 (a) (b) (c)Figure 3. Some antagonistic images of two isolates N2 GII 14 and N6 GII43.2. Secondary screening of bacterial isolates with cytotoxic activity against cancer cellsIn this study, 28 bacterial strains with antagonistic activity were further selected to screen for cytotoxic activity against 3 test cell lines: MCF-7 breast cancer cells, Hep G2 liver cancer cells, and HEK 293T normal cells. The results obtained in Table 2 show that 2/28 tested bacterial strains had quite strong cytotoxic activity against MCF-7 breast cancer cells (CSMCF-7 %u2264 50%): N1 AIA6 (CSMCF-7 = 16.5 %u00b1 0.8%) and N3 MI7 (CSMCF-7 = 50.6 %u00b1 0.6%); 3/28 strains had quite strong cytotoxic activity against Hep G2 liver cancer cells (CSHep G2 %u2264 50%) including, N1 AIA6 (CSHep G2 = 8.2 %u00b1 0.3), N3 MI7 (CSHep G2 = 24.9 %u00b1 0.9), and N3 SCA3 (CSHep G2 = 45.5 %u00b1 1.3). Most of the studied microbial strains were not toxic or had very low cytotoxicity against HEK 293T normal cells, only 1/28 strains were cytotoxic against HEK 293T normal cells (CSHEK 293T %u2264 50%). Among the three strains with cytotoxic activity against cancer cells, strains N1 AIA6 and N3 MI7 were simultaneously toxic to both tested cancer cells, but strain N1 AIA6 was not toxic to normal HEK 293T cells, while strain N3 MI7 was toxic to normal cells. Strain N3 SCA3 also had low toxicity to tested normal cells (Figure 4, Figure 5).