Intergeneric bacterial coaggregations involving mutans streptococci and oral actinomyces

Mutans streptococci (MS) representing eight different serotypes were tested for their ability to coaggregate in vitro with oral actinomyces and other streptococcal species. Of the mutans streptococci tested, only strains of S. cricetus (formerly S. mutans serotype a) displayed pronounced coaggregations and only with certain strains of actinomyces. S. cricetus coaggregated, by lactose nonreversible mechanisms, with serotype 4 Actinomyces naeslundii WVU963 and WVU924 and with serotype 2 Actinomyces odontolyticus WVU758. The first pair was disaggregated by protein denaturants (e.g., sodium dodecyl sulfate and urea) and EDTA. This coaggregation was inhibited when the streptococcal, but not the actinomyces, partner was pretreated with either heat or protease, suggesting the presence of a protein mediator on only the streptococcal cell surface. The S. cricetus-A. odontolyticus coaggregation appeared to involve protein components on each cell, as shown by the lack of coaggregation after pretreatment of either cell type with heat or proteases. This coaggregation was also reversed by sodium dodecyl sulfate and urea, as well as by sodium deoxycholate, but not by EDTA. The data indicate that different mechanisms may be involved in each of these coaggregations.