Microbiological Examination For microbiological analysis, pooled subgingival plaque samples are taken from four different teeth with at least one site with PPDs of ≥ 4 mm from each study subject. The pooled subgingival plaque sample is collected in a transport tube containing 500 µl Ringer-Glycerin-Solution. The pooled samples are at once taken to the laboratory for analysis or stored in liquid nitrogen.