The Effects of a Penicillin Dentifrice on Oral Lactobacilli

Abstract

Penicillin is known to exert an inhibitory effect on the oral lactobacilli. Hill1 re­ ported a marked decrease in salivary lactobacillus counts following the use of a penicillin dentifrice and mouthwash. After discontinuance of this regime the counts remained low for a time and then returned to their previous level. The pos­ sibility that penicillin-fastness had de­ veloped was considered but was not in­ vestigated. Thus far no reports have appeared concerning the development of resistance to penicillin by the oral lacto­ bacilli under the conditions of in vivo testing. On the other hand we have found it possible to produce penicillin-fastness in a number of human, rat and hamster lactobacillus strains in vitro by transfer­ ring large inocula of susceptible strains through media containing successively higher concentrations of penicillin. The disclosure by Zander that an ap­ parent reduction in the incidence of new caries was occurring in a group of school children using a penicillin dentifrice prompted the experiments to be described in this paper. The purpose was twofold: to determine the effect of continuous use of a penicillin dentifrice on salivary lacto­ bacillus counts, and to ascertain whether the use of such a dentifrice would result in an increased resistance to penicillin by the lactobacilli which persisted in the oral cavity.