Effect of saliva on coaggregation of oral Actinomyces and Streptococcus species

Human oral actinomyces and streptococci that exhibit specific coaggregation patterns when the cells are suspended in buffer were tested for their ability to coaggregate in saliva. Of 53 paired combinations of actinomyces (Actinomyces viscosus, A. naeslundii, or Actinomyces sp. WVa 963) and streptococci (Streptococcus sanguis or S. morbillorum) that exhibited coaggregation in buffer, all but 4 pairs also coaggregated when suspended in saliva. Twenty-four pairs exhibited lactose-inhibited coaggregation in buffer: 19 of these were identical in saliva. The other five pairs either did not coaggregate or formed coaggregates that were not inhibited by lactose. Highly specific coaggregations known to occur with buffer-suspended cells (e.g., a streptococcal strain that coaggregates with a single strain of actinomyces) were unchanged when cells were suspended in saliva. These results indicate that the coaggregation properties of both oral actinomyces and streptococci are very similar with cells suspended in either saliva or coaggregation buffer. Thus, the potential for coaggregation among bacteria in the oral cavity is evident. The possible mechanisms which mediate coaggregation in saliva are discussed.