Interest in the population genetics of bacterial systems was stimulated by several former graduate students. As this interest developed, it lead first to population studies of the tick-borne rickettsias, empahsizing use of RFLP variation to examine population structure and the population genetics of Rickettsia.  As part of these studies, species comparsions were being performed which resulted in the development of strain comparisons based on 16S rRNA. This eventually developed in an extensive study of the molecular phylogeney of the Rickettsiaceae, including 16S rRNA, 23S rRNA and surface antigen gene phylogenetic comparisons of Rickettsia, and 16S rRNA studies of members of the related intracellular group, Ehrlichia.

The analysis of the rRNA gene region allowed the development of methods to study "molecular epidemiology" and population structure of other goups of bacteria, expecially the periodontal pathogens A.a. and Porphyromonas gingivalis. By using extensions of our original rRNA gene systems developed in Rickettsia to study thes two pathogens, the variation between strains in the sequence of the spacer region between the 16S rRNA and the 23S rRNA has been used as a genetic marker.