Effects of different levels of species in mixtures on signal intensity. Aa, Aggregatibacter actinomycetemcomitans; Ao, Actinomyces odontolyticus; Cr, Campylobacter rectus; Cs, Capnocytophaga sputigena; Pe, Porphyromonas endodontalis; Pm, Parvimonas micra; Sp, Streptococcus parasanguinis.