Description of an unusual gram-negative anaerobic rod isolated from periodontal pockets

A Gram-negative rod which grew with an unusual colonial "water-drop" form was isolated from periodontal pocket samples from 12 patients. Six strains were characterized by biochemical tests, cell wall analyses, malate dehydrogenase mobilities, protein profiles, and serology. By these criteria, the organisms formed a group of similar strains which were anaerobic, nonmotile, nonsporing, Gram-negative rods resembling Bacteroides. Comparison of the isolates to American Type Culture Collection strains of Bacteroides showed that they represented a closely related group, distinct from the described species of oral Bacteroides. Initial results on the DNA of the isolates suggested a base ratio of 54-57% G + C. Despite the DNA G + C base ratios currently accepted for the Bacteroides (28-61 mol% G + C), many species fall into a narrower range of 40-52 mol% G + C. This range would exclude the organisms described here and suggests that placing them into the genus Bacteroides may be inappropriate.