Persisting virulence ofT.pallidum after incubation withpenicillin inNelson-Mayer medium

Several investigators haveshown, insyphilitic infections ofbothmanandanimals, thatafter prolonged andintensive penicillin therapy someviable organismscanstill befoundincertain bodytissues and fluids, notably thelymphnodes, cerebrospinal fluid, andaqueoushumour(Collart, Borel, andDurel, 1962;Collart andDurel, 1964;DelCarpio, 1963; Yobs,Olansky, Rockwell, andClark, 1965;Yobs, Clark, Mothershed, Bullard, and Artley, 1968; RimbaudandRoux,1965;Smith, Singer, Reynolds, Moore,Yobs,andClark, 1965;Ehrmann,1967; Smith,1969;Nicolau, Badanoiu, Nicolau, and Gavrilescou, 1969, Rice, Dunlop, Jones, Hare, King, Rodin, Mushin, andWilkinson, 1970). Although thevalidity ofthese findings hassometimesbeendoubted, thephenomenon hasbecome less debatable withtheincreasing numberofinvestigators whohaveobserved it.Thesearch foran explanation hasproduced several hypotheses. The possibility ofre-infection waseffectively ruled out inanimal experiments. Itisalso unlikely thatthese treponemes werenotallTreponema pallidum. Twofurther hypotheses maybeexplored: (1)Thatthepenicillin maynotreachadequate antibacterial levels insomeofthebodytissues or fluids. Recentinvestigation hasshownthatthisis highly unlikely. Pechere, Franceschini, andCollart (1971), using theSarcina lutea plate method(Bennett, Brodie, Benner, andKirby, 1966), havemeasured penicillin concentrations in theserum,lymph nodes, andtestes ofsyphilitic andnormalrabbits, andhaveshownthattissue concentrations, though lowerthanthoseofserum, arenonethelessadequatefortreponemicidal effect atthedoses customarily given. Penicillin concentrations ininfected testes werehigher thaninnormal testes.