Spatial arrangements and associative behavior of species in an in vitro oral biofilm model

The spatial arrangements and associative behavior of Actinomyces naeslundii , Veillonella dispar, Fusobacteridum nucleatum, Streptococcus sobrinus, and Streptococcus oralis strains in an in vitro model of supragingival plaque were determined, Using species-specific fluorescence-labeled antibodies in conjunction with confocal laser scanning microscopy, the volumes and distri bution of the five strains were assessed during biofilm formation. The volu me derived cell numbers of each strain correlated well with respective cult ure data. Between 15 min and 64 h, populations of each strain increased in a manner reminiscent of batch growth. The microcolony morphologies of all m embers of the consortium and their distributions within the biofilm were ch aracterized, as were interspecies associations. Biofilms formed 15 min afte r inoculation consisted principally of single nonaggregated cells. All five strains adhered strongly to the saliva-conditioned substratum, and therefo re, coadhesion played no role during the initial phase of biofilm formation . This observation does not reflect the results of in vitro coaggregation o f the five strains, which depended upon the nature of the suspension medium . While the possibility cannot be excluded that some interspecies associati ons observed at later stages of biofilm formation were initiated by coadhes ion, increase in bacterial numbers appeared to be largely a growth phenomen on regulated by the prevailing cultivation conditions.