In vitro study of the properties of Streptococcus mutans in starvation conditions

Objectives: The present study is to assess Streptococcus mutans survivability in different starvation conditions and to determine the resistance of starved S. mutans to lethal acid and two common anti-caries agents, sodium fluoride (NaF) and chlorhexidine acetate (CHX). Methods: S. mutans survival rates in sterile water, PBS, sterile saliva, 1/5 strength BHI and BHI were determined at a given time by plate count of viable cell. The resistance of starved S. mutans and control S. mutans to four times the minimal bactericidal concentration (MBC) of NaF, two times the MBC of CHX and acid (pH 2.8) was evaluated and compared respectively. Furthermore, field emission scanning electron microscope (FE-SEM) was used to observe the morphologic characteristics of the starved S. mutans cells. Results: S. mutans showed starvation tolerance under five different starvation conditions, but the bacterial survival rates were different at the same time points. The starved S. mutans exhibited significantly higher resistance (p < 0.05) to challenge by anti-caries agents and acid than the control S. mutans. Additionally, starvation resulted in the morphologic modification of S. mutans, and the disruptive degree depended on the change in time. Conclusion: The present study indicates that S. mutans displays starvation tolerance, and starvation decreased the susceptibility of S. mutans to NaF, CHX and acid. (C) 2011 Elsevier Ltd. All rights reserved.