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Characterization of Bacteroides melaninogenicus and its role in mixed anaerobic infections Mayrand, Denis


The pigmented oral BacterOides were characterized with regard to their pathogenic, collagenolytic, hemagglutinating and metabolic properties. Isolates were obtained from healthy and diseased gingival sulci of 396 children, adults and mongrel dogs. Fifty-three of the isolates proved to be members of the subspecies Ii. melaninogenicus ss. asaccharolyticus. The remainder were either 15. melaninogenicus ss. intermedius or melaninogenicus. All isolates designated asaccharolyticus were pathogenic in the guinea pig infectivity assay. The subspecies intermedius and melaninogenicus were not pathogenic. The subspecies asaccharolyticus possessed a cell bound oxygen sensitive collagenase, a cell bound and soluble oxygen sensitive hemagglutinin, and produced butyric and phenylacetic acids. These properties were unique to asaccharolyticus and were not detected with other organisms. All isolates required hemin. The pathogenic organisms possessed a heat sensitive toxin which induced fluid accumulation in ligated mouse ileal loops. Infectivity of 13. melaninogenicus asaccharolyticus was dependent on the presence of a second organism. An infective consortium consisting of 13. melaninogenicus 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 number and proportions of J3. melaninogenicus and K. pneumoniae required to establish a lesion was determined. The nature of the infection appeared to be determined by the length of the lag period preceding the initiation of growth of 15. melaninogenicus. 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. J3. melaninogenicus 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 oh 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 JJ. tnelahinogenicus 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 13. melaninogenicus together with agar-immobilized succinate or hemin. Growth of Ii. melaninogenicus is dependent on the presence of large quantities of succinic acid suggesting that the compound is used in energy metabolism and is not incorporated into cellular carbon. This assumption is supported by the observation that only 0.5% of the succinate carbon can be found in the cell, the remainder of the metabolized succinate is excreted as butyrate. Hemin blocks the metabolism of succinate. The fatty acid metabolites are qualitatively similar but quantitatively different in cells grown in hemin free succinate medium.

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