A Study of the Action of Antibiotics in Vitro on Microorganisms Isolated from Root Canals

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Abstract
51 cultures of oral microorganisms were studied for their resistance or susceptibility to the 2 antibiotics, penicillin and streptomycin. 28 of these cultures were streptococci, and most of the spp. of non-hemolytic streptococci recorded in the literature were represented in our series by at least 1 culture. The exception is the so-called s.b.e. streptococcus of Niven, Kiziuta and White, which they found to be more frequently associated with subacute bacterial endocarditis than other nonhemolytic streptococci. Many of the nonhemolytic streptococci found by the authors were not satisfactorily identified, but none showed the viscous growth on 5% sucrose tryptone yeast extract which is characteristic of the s.b.e. streptococcus. Of the 28 streptococci, only 6 showed marked resistance to penicillin or streptomycin or both. These were the 2 entero-cocci (S.fecalis and S. liquefaciens), S. equinus, S. salivarius, 1 culture of S. mitis and of S. bovis. The fecalis was outstanding in its resistance to both antibiotics. The lacto-bacilli, of which 7 cultures were isolated, showed considerable resistance to penicillin, and when lactobacilli and streptococci were mixed, the resistance of the mixture was very much greater than that of pure cultures of either organism.

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