The effect of surfactants upon the activity and distribution of glucosyltransferase in Streptococcus mutans 6715

A modified Somogyi-Nelson procedure was used to determine the amount of reducing sugar produced during the reaction of S. mutans 6715 glucosyltransferase (GTF) with sucrose. This technique is an indirect measure of GTF activity and was used to determine the effects of the surfactants glycerol monolaurin (GML) and sodium lauryl sulfate (SLS) upon crude extracellular GTF. GML at 5, 10, and 15 micrograms/ml reduced culture filtrate GTF enzyme activity to an average of 81% of the control value. SLS at the only concentration tested (15 micrograms/ml) also caused a reduction, resulting in a GTF activity level that was 82% of the control value. Secondly, S. mutans 6715 cultures were grown in a medium containing Tween 80, or SLS. The cell-free culture filtrate and the cell-pellet were assayed separately for GTF activity. GML in the medium produced a decrease in culture filtrate GTF activity and an increased cell-pellet activity. The total (whole culture) activity for culture broths was 89% to 90% of the control value when 5, 10, or 15 micrograms/ml GML were added. Tween 80 supplemented culture medium resulted in increased culture filtrate GTF, while levels measured in the cell-pellet were decreased. Overall, Tween 80 caused a large increase in whole culture GTF activity. Cell cultures containing SLS at 15 micrograms/ml resulted in no change in the GTF activity as compared to the control, nor was there any change in the percent of GTF in the culture filtrate versus the percent which was in the cell-pellet. Higher concentrations of SLS could not be tested due to the inhibitory effect on cellular growth.