Porphyromonas gingivalis in Maxillary and Salivary Tissue of Gavaged Mice.

Objectives: Porphyromonas gingivalis (P.g.) infects gingiva and promotes periodontal disease in humans. It may also contribute to salivary gland disease via infection of salivary gland tissues. To study host-pathogen interactions in vivo, P.g. may be introduced into laboratory mice by oral gavage. The goal of this study was to develop a qPCR assay to quantify the number of P.g. bacteria within maxillary tissues containing gingiva, and in salivary glands, of P.g.-treated mice. We hypothesize that qPCR will detect a high number of P.g. in maxillary tissue, and few or no P.g. in salivary glands of mice administered P.g. via oral gavage.
Methods: To establish a standard curve for quantification of P.g., a dilution series of known quantities of cultured P.g. DNA, ranging from 10⁶ genomes to single copy, was analyzed by non-nested and nested qPCR. To generate mice with P.g. infected oral tissues, conventionally housed mice without antibiotic treatment were administered P.g. (n=6) or control vehicle (n=5) by oral gavage, once per day for 10 days. At the end of treatment, palate tissues and salivary glands were harvested, and DNA was prepared. Nested qPCR was performed, and the amount of P.g. DNA obtained was determined by comparing the qPCR value with the standard curve.
Results: Consistent with the fact that untreated mice do not normally have P.g., P.g. was not detected in any control vehicle treated mice. In contrast, bacterial DNA was detected in maxillary tissue of mice administered P.g. The number of P.g. genomes detected in maxillary tissue was low and variable between animals, suggesting that further assay optimization is needed to enumerate bacteria isolated from tissues. P.g. was not detected in salivary glands.
Conclusions: Using a qPCR standard curve it is possible to quantify P.g. genomes from oral tissues. However, accurate quantification of P.g. from within mammalian tissues may require additional optimization.