Effects of pH, potassium, magnesium, and bacterial growth phase on lysozyme inhibition of glucose fermentation by Streptococcus mutans 10449.

The effects of physiological (saliva and plaque fluid) concentrations of potassium and magnesium and growth phase on lysozyme inhibition of glucose fermentation by S. mutans 10449 were investigated. Glucose fermentations were carried out in a pH-stat at pH 7.0 or 5.5. Cells were at least two times more sensitive to lysozyme in the early-to-middle exponential phase compared with the stationary phase. S. sobrinus 6715 exhibited three-fold greater lysozyme resistance than S. rattus BHT or S. mutans 10449. The concentration of potassium which reduced lysozyme inhibition of S. mutans 10449 fermentation by 50% was 0.2 and 10 mmol/L for stationary and exponential phase cells, respectively. Corresponding values for magnesium were < or = 0.01 and 0.50 mmol/L. Potassium and magnesium exhibited little pH dependence in their reduction of lysozyme inhibition of fermentation by exponential- or stationary-phase S. mutans 10449. The results suggest that: (i) lysozyme interaction with stationary-phase cells involves more non-inhibitory modes than with exponential-phase cells, and (ii) lysozyme may be more effective as an antibacterial agent in saliva than in plaque fluid.