This in vitro study was designed to test the hypothesis that sampling of bacterial suspensions by absorbent paper points would accurately reflect the proportion of the bacterial species whether they are homogeneously or non-homogeneously distributed in the sample site. The non-homogeneously distributed populations consisted of equal numbers of colony forming units (CFU) of two periodontal bacterial species present as separate cultures, one layered on top of the other. The species in the top layer accounted for greater than 90% of the total number of CFU detected by paper point sampling, regardless of which species formed the top layer. In contrast, when the layers were mixed prior to sampling to give a homogeneous bacterial distribution, the paper points detected equal numbers of CFU of each species. Thus the hypothesis was not supported and the proportions yielded by paper point sampling are not the same when the bacteria are non-homogeneously distributed as when they are homogeneously distributed. Ultrastructural observations have documented a non-homogeneous distribution of bacterial species in periodontal pockets. If the specific microbiota in the apical portion of deep periodontal pockets are important to the periodontal disease process, these data suggest that bacterial samples obtained by absorbent paper points misrepresent the presence of such bacterial species.
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