Effect of Saliva/Bacteria from Aggressive Periodontitis Patients on Streptococcus mutans

Objectives: Aggregatibacter actinomycetemcomitans (Aa) is associated with Aggressive Periodontitis (AgP). Previous studies indicated that AgP patients had minimal proximal caries. The aim of this research was to investigate the effect of Aa-positive AgP patients saliva, and the effect of Aa spent culture medium (SCM), on Streptococcus mutans (Sm) in vitro growth. Methods: Unstimulated saliva was collected from 12 Aa-positive AgP patients and plated for Aa isolation on TSBV agar. Aa colonies were grown in 2 different volumes in order to obtain Aa SCM. The Aa SCM, as well as filtered saliva from Aa-positive AgP patients, were tested for antimicrobial activity on Sm suspension, as compared to: sterile saliva from a healthy individual, Aa culture medium, Sm spent culture medium, and sterile Sm medium. Antibacterial activity was checked by turbidimetric determination of Sm bacterial growth in a microtiter plate, and bacterial growth curves were obtained. Results: Aa SCM inhibited Sm growth, as expressed in the growth curve slopes, compared to the control groups (P <0.05). Sm bacterial Optical Density after 24h was the lowest in the test groups as compared to the controls. The filtered saliva from Aa-negative and Aa-positive patients had an inhibitory effect on Sm, which was not significantly different. However, filtered saliva from Aa-positive patients displayed lower bacterial densities at the stationary phase as compared to that of Aa-negative individual. Conclusion: Aa bacteria from AgP Aa-positive patients produced factor/s which inhibited Sm growth in vitro, thus may explain why AgP patients have less proximal caries. The inhibitory effect of Aa SCM was mainly expressed during the exponential growth phase. Hence, the inhibition occurs in a bacteriostatic manner.