Frederick Griffith - Griffith's Experiment

Griffith's Experiment

Pneumococci has two general forms—rough (R) and smooth (S). The S form, considered virulent, bears a capsule, which is a slippery polysaccharide coat—atop and outside the peptidoglycan cell wall common among all classical bacteria—enhances bacterial evasion of efficient phagocytosis by the host's innate immune cells. Injected subcutaneously with S form, mice succumbed to pneumonia and death within a couple of days. The R form, however, lacking a capsule—its outer surface being cell wall—was considered avirulent, not prompting pneumonia.

When Griffith injected heat-killed S into mice, as expected no disease ensued. When mice were injected with a mixture of heat-killed S and live R, however, pneumonia and death ensued. The live R had transformed into S—and replicated as such—often characterized as Griffith's Experiment. More accurately, point six of Griffith's abstract reports that R tended to transform into S if a large amount of live R, alone, were injected, and that adding much heat-killed S made transformation reliable Griffith also induced some pneumococci to transform back and forth.

Griffith also reported transformation of serological type—bacterial antigenicity—distinct from presence or absence of a capsule. Bacteriologist Fred Neufeld, of the Robert Koch Institute in Berlin, Germany, had earlier identified the pneumococcal types, confirmed and expanded by Alphonse Dochez at Oswald Avery's laboratory in America at The Rockefeller Hospital. Types I, II, and III were each a distinct antigenic grouping, whereas type IV was a catchall of varying antigenicities not matching other types.

Illustrating S pneumoniaes plasticity, the abstract of Griffith's paper reports, "The S form of Type I has been produced from the R form of Type II, and the R form of Type I has been transformed into the S form of Type II".