Effects of Streptococcus crista and human saliva on the viability of Fusobacterium nucleatum ATCC 10953

Associations with facultative species might help planktonic oral anaerobes survive when they traverse saliva. This study investigated whether co-aggregation with Streptococcus crista ATCC 51110 enhanced the viability of Fusobacterium nucleatum ATCC 10953. Two tubes each of co-aggregates and Fus. nucleatum ATCC 10953 alone were prepared. One of each set was resuspended in buffer, and the other in clarified saliva from each of 20 donors. After 1 h, cells were stained for viability. The median percentage of viable Fus. nucleatum ATCC 10953 in buffer with Strep. crista (86%) was significantly higher (p=0.04) than in buffer alone (77%). A similar trend was observed for saliva with Strep. crista (81%) and saliva alone (74%), although that difference was not significant (p=0.41). The median percentage of Fus. nucleatum co-aggregated in buffer (44%) was significantly reduced after incubation in saliva (16%) (p<0.0002). No such change was seen when saliva was replaced with purified salivary proline-rich glycoprotein, which can bind both species. For co-aggregate suspensions, there was no difference in the viability of fusobacteria that were or were not in direct contact with Strep. crista. In both cases, viability was significantly reduced in saliva relative to buffer. Strep. crista may enhance the viability of planktonic Fus. nucleatum ATCC 10953, but it is not yet clear whether that requires co-aggregation. Transmission of fusobacteria through saliva could depend on the interplay between protective factors, such as the presence of streptococci, and antimicrobial factors, which kill cells or disassociate co-aggregates.