Method: So34, SgDL1 and the isogenic SgDL1 coaggregation deficient mutants, SgsspAB, SgcshAB and SgsspABcshAB were cultured in Schaedler or CAMG medium to mid-exponential phase. Cells were washed in coaggregation buffer and diluted to an OD of 1.0 at 600nm. Interspecies crosses were performed in each media and across media, and coaggregation strength was assessed using the standard visual coaggregation assay. To confirm visual findings, we also quantified coaggregation between the cells grown in Schaedler and CAMG media based on particle diameter using FlowCAM technology. The ability of lactose and arginine to inhibit coaggregation was also assessed.
Result: Cells grown in Schaedler medium showed strong (score of 4+) coaggregation between So34 and SgDL1 and SgsspAB; this was inhibited by the addition of arginine but not by lactose. In CAMG medium there was less strong coaggregation between So34 and SgDL1 (3+), but not between So34 and SgsspAB, the interaction was inhibited by the addition of arginine or lactose. FlowCAM technology confirmed these results; the rate of coaggregate formation was culture medium dependent. When crosses were performed across media, So34 from Schaedler medium coaggregated strongly (3+) with SgDL1 and SgsspAB grown in CAMG. Coaggregation was slightly weaker (2-3+) when the growth media were reversed. In both cases coaggregation was inhibited only by arginine.
Conclusion: Culturing in different media affects coaggregation. Such differences may relate to the differential expression of coaggregation adhesions that naturally occur during dental plaque development.