Proteolysis and utilization of albumin by enrichment cultures of subgingival microbiota

Subgingival dental plaque consists mainly of microorganisms that derive the ir energy from amino acid fermentation. Their nutrient requirements are met by the subgingival proteolytic system, which includes proteases from micro organism and inflammatory cells, and substrate proteins from sulcus exudate , including albumin. To determine the selective effect of individual protei ns on microbiota, we used albumin as the main substrate for growth. Eight s ubgingval plaque samples from untreated periodontal pockets of patients wit h adult periodontitis were inoculated in peptone yeast medium with bovine a lbumin (9 g/l). After three subculture steps, cell yields of the enrichment cultures at the medium with 0, 1.25, 2.5, 5, 10, and 20 g/l albumin were d etermined. Proteolytic activity (U/absorbance at 550 nm) of the enrichment cultures and different isolates derived from the cultures was estimated by the degradation of resorufin-labeled casein. It was observed that the yield of the mixed culture was albumin limited, and the proteolytic activities o f the cultures in albumin broth were higher than in control (peptone broth) . Among the isolates from the enrichment cultures, Peptostreptococcus micro s, Prevotella melaninogenica, Prevotella buccae and Prevotella bivia demons trated proteolysis. The frequent occurrence of Streptococcus gordonii and S treptococcus anginosus in the albumin cultures is explained by their abilit y to utilize arginine as an energy source for growth. Albumin in the medium was partly degraded by pure cultures but completely consumed in enrichment cultures, indicating synergy of bacterial proteinases. It is concluded tha t the subgingival microbiota possesses proteolytic activity and may use alb umin as a substrate for their growth. Enrichment cultures on albumin may se rve as a relatively simple in vitro model to evaluate the effects of protei nase inhibitors.