Penicillin Sensitivity of Streptococci Isolated from Root Canal Infections and the Normal Mouth

Abstract

Many workers have shown that certain strains of supposed penicillin-sensitive bacteria may be resistant to penicillin. Since a clinical study of the effect of penicillin in infected root canals was contemplated it was thought desirable to ascertain the sensitivity of individual strains of streptococci, which are the organisms commonly isolated from infected root canals. At the same time it was decided to determine the reactions to penicillin of streptococci from saliva of normal mouths. As it has been presumed that the streptococci causing root canal infections are usually derived from the saliva, the reactions of streptococci from the two sites might lead to some information on their relationship.Material from infected root canals was inoculated into beef infusion semi-solid agar, containing ascitic fluid. The cultures after incubation at 37.50C. for 36-48 hours were plated out on 2% blood agar. Single colonies of streptococci were then transferred to other blood agar plates to be studied. The reaction on blood was determined, and the streptococci classified as hemolytic, viridans or anhemolyticus. No other method or classification was attempted, since the viridans and anhemolytic types form such heterogenous groups that it was not thought expedient at this time to attempt further classification. The hemolytic group of streptococci are recovered in only 2% of infected root canals.Streptococci from saliva were obtained from individuals who had no mouth infections. The saliva after collection was diluted with physiological salt solution, so that discrete colonies grew when streaked on blood agar. Single colonies were transferred to blood agar for study. No difficulty was encountered in identifying viridans type of streptococci, but difficulty was encountered with hemolytic and anhemolytic types of streptococci. It was noticed that colonies which had been picked as hemolytic types after replating, were anhemolytic in type; or that the anhemolytic type was hemolytic. At first it was thought that errors had been made in identifying colonies, but it happened so frequently, and after further precautions had been taken that we realized that we were dealing with dissociated strains, which had to be replated several times to obtain pure phase cultures. This particular problem is to be investigated in the near future.Tryptose broth (1) containing 5% ascitic fluid, and penicillin sodium was used to carry out the penicillin sensitivity tests. Strains were tested in 0.03 U, 0.5 U. and 8 U. of penicillin per c.c. of broth. A positive control was made in the 1