In his transformation experiments, what phenomenon did Griffith (1928) observe? September 21, 2022 by 8i9x6 Mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form. Mixing a heat-killed nonpathogenic strain of bacteria with a living pathogenic strain makes the pathogenic strain nonpathogenic. Infecting mice with nonpathogenic strains of bacteria makes them resistant to pathogenic strains. Mice infected with a pathogenic strain of bacteria can spread the infection to other mice. See Answer Mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.