Stimulation of the growth of Streptococcus sanguis (NCTC 7864) by zinc in vitro

Zinc, which is present in many materials used in dentistry, including restorative and endodontic materials and mouthwashes, is reputedly bactericidal. However, the addition of this element at concentrations in the range 10-50 ppm to cultures of Streptococcus sanguis (NCTC 7864) stimulated the growth of the micro-organism relative to that of controls. A second antibacterial element, namely fluoride, reduced growth. Similar results were obtained whether the organism was grown aerobically or anaerobically. In view of the susceptibility of some organisms to zinc, the results of this study may help to explain conflicting reports in the literature; the results will vary depending on which organism is predominant.