Recovery of A. actinomycetemcomitans Strains Inoculated Into the Mouths of Rhesus Monkeys

Objectives: The goal of these experiments was two-fold; 1) to develop a model that would allow for assessment of the impact of doxycycline on repopulation of the oral cavity with commensal bacteria, as well as 2) the quantitative recovery of Spectinomycin labeled A. actinomycetemcomitans (Aa) strains inoculated into the mouths of Rhesus (Rh) monkeys treated by mechanical cleaning as compared to doxycycline treatment.
Methods: Initial efforts were designed to reduce competition from the existing Rh monkey commensal oral flora by mechanical cleaning as compared to mechanical cleaning plus use of systemic doxycycline. The study groups consisted of 11 Rh monkeys in the doxycycline group and 15 monkeys in the mechanical cleaning group. Next generation sequencing was used to determine the qualitative and quantitative distribution of members of the oral flora at baseline, post- treatment, and 4-5 weeks after inoculation of Spectinomycin (Sp) labeled Aa. Culture was used to recover Sp resistant Aa strains. Likely consortia known to associate with Aa were also assessed using sequencing methods.
Results: Results indicated that recovery in the mechanical cleaning group occurred as expected and both indigenous Aa and Sp labeled Aa were found 2 and 4 weeks after cleaning. Sp labeled Aa was only seen at 4 weeks post inoculation and at low levels in the doxy group. In contrast indigenous Streptococcus gordonii levels were elevated at all times post treatment in the doxy treated group as compared to the mechanically treated group while indigenous Aa was found at lower levels in the doxy treated group. An association of Aa and S. gordonii was favored at all times and in both treatment groups when compared to Filifactor alocis and S. parasanguinis.
Conclusions: These results illustrate that Aa and other members of the commensal oral flora can associate in a similar manner to that seen in humans. Moreover, a short course of doxycycline treatment expected to enable Aa colonization appeared to interfere with colonization of Sp labeled Aa strains in this monkey model. This model may be capable of examining the potent impact of antibiotics on microbial community organization and behavior.