By injection into
typhus-infected yolk sacs, a number of agents were tested for possible inhibition or acceleration of rickettsial growth. The previously reported rickettsiostatic activity of
penicillin was further confirmed.
Para-aminobenzoic acid, in single
injections of 6.6 mg. and 3.3 mg. giving initial concentrations of approximately 1:6000 and 1:12,000 was found to have rickettsiostatic activity approximately equal to that of
penicillin. No conclusion could be drawn regarding the possibility of a synergistic action of
para-aminobenzoic acid and
penicillin.
Para-aminobenzoic acid neutralized with
sodium hydroxide was found to be as effective as the
acid itself, when given in single
injections of 6.6 mg.
Sodium benzoate, as Well as the ortho and meta forms of aminobenzoic
acid were found to be ineffective when given in similar amounts.
Para-aminobenzoic acid, when added to the food in a concentration of 3 per cent, was shown to have a remarkably effective chemotherapeutic action on
murine typhus infection in mice.
Sodium fluoride was found at times to accelerate the growth of rickettsiae in the yolk sac, and to cause heavy
infection under conditions such that the controls showed practically no multiplication of the organism. When rickettsiostatic substances (
penicillin and
para-aminobenzoic acid) were combined with
sodium fluoride, their rickettsiostatic activity was not demonstrably changed. Other agents studied and found not to affect rickettsial multiplication are listed. The possible mechanisms involved in the observed inhibition and stimulation of rickettsial growth under these conditions are discussed.