Biochemical change exhibited by oral streptococci resulting from laboratory subculturing

The intent of this study was to assess the effects of continued laboratory subculturing on selected biochemical properties of oral streptococci freshly isolated from dental plaque. Six fresh isolates (3 Streptococcus mutans and 3 non-mutans) and 2 laboratory strains were subcultured daily for a total of 225 transfers, and cells were harvested every 75 transfers from duplicate batch cultures grown with glucose at a constant pH. Eleven biochemical properties were assayed with cells, membranes and cell-free extracts and the results subjected to statistical analysis for differences between the duplicate cultures and the various subcultures. In addition, the activity of 19 hydrolytic enzymes was assayed with the semiquantitative apiZYM system (Analytab products). The activity of zero-time samples varied by as much as 241-fold for a single property with particularly low activity for EIIglc of the phosphoenolpyruvate phosphotransferase system and cell-associated extracellular polysaccharide synthesis. The 3 S. mutans fresh isolates had higher activity in 8 of the 11 assays compared with the 3 non-mutans strains, with extracellular polysaccharide synthesis the most significant trait. Statistical analysis of the 2816 assays of the 11 traits for the 8 test strains at the 4 selected time intervals revealed considerable change in the activity of the test parameters. The most notable changes in the S. mutans strains over the 225 subcultures were significant increases in glycolytic activity and decreases in hydrophobicity and extracellular polysaccharide synthesis activity. Of the measured properties, lactate dehydrogenase and cell-associated extracellular polysaccharide synthesis activity were the most stable and H+/ATPase activity was the most variable.(ABSTRACT TRUNCATED AT 250 WORDS)