Effect of encapsulated Bacteroides asaccharolyticus and Bacteroides fragilis on the growth of aerobic and facultative bacteria in mixed infections.

The effects of encapsulation of Bacteroides asaccharolyticus and Bacteroides fragilis on aerobic or facultative bacteria were evaluated using a subcutaneous abscess model in mice. The change in number of aerobic and facultative bacteria (AFB) was studied by comparing their number when injected with nonencapsulated, encapsulated Bacteroides species, and capsular material of Bacteroides species. In 14 combinations of AFB mixed with nonencapsulated Bacteroides species, an increase in the number of nonencapsulated Bacteroides species and an increase in the number of AFB occurred in two instances. An increase in the number of AFB occurred in 11 of the 14 combinations with encapsulated Bacteroides species. No change in the bacterial numbers was observed when the AFB were inoculated with capsular material of Bacteroides species. These data demonstrate the ability of viable encapsulated Bacteroides species to enhance the growth of aerobic or facultative bacteria.