Exological relationships of bacteria involved in a simple, mixed anaerobic infection.

Infectivity of Bacteroides asaccharolyticus (formerly B. melaninogenicus subsp. asaccharolyticus; see S. M. Finegold and E. M. Barnes, Int. J. Syst. Bacteriol. 27:388--391, 1977) was dependent on the presence of a second organism. An infective consortium consisting of B. asaccharolyticus and Klebsiella pneumoniae was defined. Neither organism was infective alone, but the Klebsiella could be replaced by organisms of a number of different genera. The nature of the infection appeared to be determined by the length of the lag period preceding the initiation of growth of B. asaccharolyticus. A rapid onset of growth led to the severe spreading form of the disease, whereas a slow initiation of growth resulted in the formation of a localized, self-limiting abscess. B. asaccharolyticus depends on the second or "helper" organism to produce a required growth factor which is not present at the inoculation site. The growth factor was shown to be succinate which was able to replace the hemin requirement. The dependency on succinate produced by K. pneumoniae was demonstrated in agar medium, in liquid culture, and in the infectivity assay. Any organism which produced succinate was able to stimulate growth of B. asaccharolyticus on agar medium and could replace K. pneumoniae as a member of the infectious consortium. The need for the second organism could be eliminated by inoculating B. asaccharolyticus together with agar-immobilized succinate or hemin.