PROTEIN-DEGRADATION BY PREVOTELLA-INTERMEDIA AND ACTINOMYCES-MEYERI SUPPORTS THE GROWTH OF NON-PROTEIN-CLEAVING ORAL BACTERIA IN SERUM

The proteolytic activities of oral bacteria are thought to play an imp ortant role in the aetiology of dental abscesses. Bacteria-derived pro teases may contribute to tissue destruction, and are likely to impair host defence by degrading immunoglobulins and complement. Degraded per iodontal tissue and tissue fluid are likely to constitute essential so urces of nutrients in the abscess. Tissue fluid, which is derived from serum, is rich in protein and poor in carbohydrate, suggesting that b reakdown of protein and fermentation of amino acids is a crucial step to generate energy for growth of the microflora. The number of oral ba cterial species that perform hydrolytic cleavage of protein into polyp eptides, the first step in protein degradation, is relatively small co mpared to the large majority of peptidase-producing species. In this s tudy, we therefore investigated the growth-promoting effect of protein ase-producing species like Prevotella intermedia and Actinomyces meyer i on the growth of some non-proteinase producing bacteria in mixed cul tures. We used serum as a substitute for the supposed natural substrat e of the abscess microflora. The breakdown of serum proteins was inves tigated using capillary electrophoresis. Poor growth was found in mono - and mixed cultures of non-proteinase producing species Eubacterium l entum, Fusobacterium nucleatum, Peptostreptococcus micros and Streptoc occus intermedius. The presence of P. intermedia in mixed cultures str ongly enhanced growth of these 4 species, according to the hypothesis that the growth of the mixed cultures was peptide-limited. The enhance d growth of P. intermedia in pronase-digested serum indicated peptide- limited growth of this organism in serum, despite its production of pr oteinase. We found that growth of monocultures of Actinomyces meyeri w as poor. In contrast, A. meyeri grew well in mixed cultures and its pr esence stimulated growth of F. nucleatum and P. micros, suggesting a s ynergistic relationship. The growth of mono- and mixed cultures was in vestigated using one representative strain of each species. Thus, ther e is a small risk of having selected unique strains. Proteinase inhibi tors reduced the growth of Porphyromonas gingivalis, Prevotella nigres cens, and P. intermedia in trypticase peptone-yeast extract medium wit h, and without, IgG. Our study indicated that proteinase-producing org anisms play a key role in mixed cultures of oral bacteria in human ser um by providing polypeptides for growth. This may explain their associ ation with dental abscesses.