1909-1972

Canadian bacteriologist whose research with Oswald Avery determined that DNA was the molecular agent responsible for transforming harmless avirulent bacteria into disease-causing virulent bacteria. Macleod and his colleagues isolated DNA from heat killed, virulent Streptococcus pneumoniae and exposed it to living, avirulent cells. The DNA from the dead, virulent cells was able to transform the live, harmless strains into encapsulated virulent ones. The ability to absorb and incorporate DNA from dead bacteria occurs in several important bacterial genera and involves traits such as encapsulation, pathogenicity, and drug resistance.