Abstract
The growth of Streptococcus mutans was inhibited by 1.5% sodium citrate added to some basal media. Such inhibition was also recognized in trypticase soy broth medium containing 5% sucrose and 1.5% citrate. Sodium citrate had no inhibitory effects on the growth of any other streptococcal type strain (S. sanguis, S. salivarius, S. mitis, S. MG, Group A S. pyogenes, or Group K streptococci) or Staphylococcus aureus.
When added to trypticase soy broth medium where S. mutans had been incubated, sodium citrate showed an inhibitory effect on the streptococcal growth in the early stage. No such inhibition was observed in a culture medium which contained sodium citrate and to which divalent cations, such as Mn++, Ca++, and Mg++, had been added. EDTA, a potent chelating agent, was also able to inhibit the growth of S. mutans. Sodium citrate did not inhibit glucose utilization by S. mutans.
Sodium citrate inhibited the growth of 96-100% of the strains which had been isolated from the dental plaques of healthy individuals and from carious lesions and which had fermented both mannitol and sorbitol. It did not inhibit the growth of 70% of the strains which failed to ferment mannitol and sorbitol.
From these results, it seems that sodium citrate may have inhibited the growth of S. mutans, since it has a chelating activity on divalent cations which are essential for the growth of S. mutans. In addition, these findings suggest that the failure of growing in the presence of sodium citrate may be one of the biological and biochemical properties of S. mutans useful for the identification of this organism.
