CO ADHESION OF ORAL MICROBIAL PAIRS UNDER FLOW IN THE PRESENCE OF SALIVA AND LACTOSE

Co-aggregation (interactions between two suspended micro-organisms) be tween oral microbial pairs has been studied extensively and is believe d to be an important factor in dental plaque formation. However, coadh esion (interactions between suspended and already-adhering micro-organ isms) may well be equally important. The aim of this paper was to dete rmine the influence of saliva and lactose on the co-adhesion of strept ococci (S. oralis 34 and S. sanguis PK1889) to actinomyces (A, naeslun dii T14V-J1 or 5951) adhering on glass under flow from buffer and sali va in the absence and presence of lactose. The kinetics of co-adhesion as well as co-adhesion in a stationary end-point of co-aggregating an d non-co-aggregating pairs was studied in a parallel plate flow chambe r by analysis of the spatial arrangement of co-adhering micro-organism s as a function of time. For co-aggregating pairs, initial deposition rates of streptococci in the immediate vicinity of adhering actinomyce s (local initial deposition rates) were up to 5 to 10 times higher tha n the non-local initial deposition rates in buffer and in saliva, resp ectively. In a stationary end-point of co-adhesion, 5 to 6 times more streptococci co-adhered with the adhering actinomyces than averaged ov er the entire substratum surface. A non-co-aggregating pair showed onl y minor preferential (co-)adhesion near the adhering actinomyces. Go-a dhesion in buffer was fully lost when lactose was added. However, addi tion of lactose to saliva did not inhibit co-adhesion, but co-adhesion became more reversible. Detachment of micro-organisms from the substr atum due to the passage of an air-liquid interface, as occurs in the o ral cavity during eating, drinking, and speaking, was minimal when dep osition was carried out from buffer to bare glass. Major detachment of streptococci adhering to the substratum occurred when adhesion was me diated through a salivary conditioning film on the glass, while detach ment of adhering actinomyces and streptococci co-adhering with them re mained low. It is suggested that, in the development of dental plaque, adhering actinomyces may act as strongholds for other micro-organisms , like streptococci, to adhere.