PPLO of human genital origin; serological classification of strains and antibody distribution in man.

Pleuropneumonia-like organisms (PPLO) have frequently been isolated from the human genital tract since the first report by Dienes and Edsall (1937); their presence in the urethral discharge of patients with non-gonococcal urethritis (N.G.U.) aroused interest because of the unknown aetiology of the disease. The significance ofPPLO in the genital tract and their association with N.G.U. are disputed. The subject has been critically reviewed by Harkness (1950), Edward (1954), and more recently by Klieneberger-Nobel (1959), who also described cultural studies made concurrently with the work reported here. Beveridge, Campbell, and Lind (1946) detected complement-fixing antibodies to human genital PPLO in human sera, but found no association between their presence and concurrent urethritis. Harkness and Henderson-Begg (1948) could not detect antibodies in any of 25 N.G.U. patients and 25 controls, even though PPLO were isolated from fifteen of the first group. PPLO isolated from the blood of a woman with puerperal fever, from an empyema wound, and from the genital system of two other women were considered by Stokes (1955) to be the cause of clinical infection in those patients; PPLO antibody appeared in the sera, increased during the *course of the infection, and had decreased 6 months later. Melen and Gotthardson (1955) made similar observations in five cases of salpingo-oophoritis. Pathogenic members of the pleuropneumonia group of organisms also induce antibody formation in animals of various species. Antibodies appear in contagious pleuropneumonia of cattle and in contagious agalactia of sheep; and may be detected by complement-fixation tests as an aid to the diagnosis of those diseases (Campbell and Turner, 1936; Zavagli, 1951). Serological tests with an appropriate PPLO antigen offer an obvious way to determine the significance of PPLO in human urethritis. The antigen, however, must be representative of the infecting strains. Accordingly, a survey was made of 56 of the 98 strains isolated by Dr. Klieneberger-Nobel from