Avery, Oswald Theodore (1877–1955)

Canadian-born US bacteriologist. His work on transformation in bacteria established in 1944 that DNA (deoxyribonucleic acid) is responsible for the transmission of heritable characteristics. He also proved that polysaccharides play an important part in immunity.

Avery was born in Halifax, Nova Scotia, but spent most of his life in New York. He studied medicine at Columbia University, and worked at the Rockefeller Institute Hospital 1913–48.

Avery's work on transformation – a process by which heritable characteristics of one species are incorporated into another species – was stimulated by the research of F Griffith (1877–1941), who 1928 published the results of his studies on Diplococcus pneumoniae, a bacterium that causes pneumonia in mice.

Avery proved conclusively that DNA was the transforming principle responsible for the development of polysaccharide capsules in unencapsulated bacteria that had been in contact with dead, encapsulated bacteria. This implicated DNA as the basic genetic material of the cell.

Avery's early work also involved pneumococci, but was in the field of immunology. He demonstrated that pneumococci bacteria could be classified according to their immunological response to specific antibodies and that this immunological specificity is due to the particular polysaccharides that constitute the capsule of each bacterial type. This research established that polysaccharides play an important part in immunity and led to the development of sensitive diagnostic tests to identify the various types of pneumococcus bacteria.