Persisting virulence of T. pallidum after incubation with penicillin in Nelson-Mayer medium.

Several investigators have shown, in syphilitic infections of both man and animals, that after prolonged and intensive penicillin therapy some viable organisms can still be found in certain body tissues and fluids, notably the lymph nodes, cerebrospinal fluid, and aqueous humour (Collart, Borel, and Durel, 1962; Collart and Durel, 1964; Del Carpio, 1963; Yobs, Olansky, Rockwell, and Clark, 1965; Yobs, Clark, Mothershed, Bullard, and Artley, 1968; Rimbaud and Roux, 1965; Smith, Singer, Reynolds, Moore, Yobs, and Clark, 1965; Ehrmann, 1967; Smith, 1969; Nicolau, Badanoiu, Nicolau, and Gavrilescou, 1969, Rice, Dunlop, Jones, Hare, King, Rodin, Mushin, and Wilkinson, 1970). Although the validity of these findings has sometimes been doubted, the phenomenon has become less debatable with the increasing number of investigators who have observed it. The search for an explanation has produced several hypotheses. The possibility of re-infection was effectively ruled out in animal experiments. It is also unlikely that these treponemes were not all Treponema pallidum.