The establishment of reproducible, complex communities of oral bacteria in the chemostat using defined inocula

Nine commonly isolated oral bacterial populations were inoculated into a glucose-limited and a glucose-excess (amino acid-limited) chemostat maintained at a constant pH 7.0 and a mean community generation time of 13.9 h. The bacterial populations were Streptococcus mutans ATCC 2-27351, Strep. sanguis NCTC 7865, Strep. mitior EF 186, Actinomyces viscosus WVU 627, Lactobacillus casei AC 413, Neisseria sp. A1078, Veillonella alkalescens ATCC 17745, Bacteroides intermedius T 588 and Fusobacterium nucleatum NCTC 10593. All nine populations became established in the glucose-limited chemostat although Strep. sanguis and Neisseria sp. were present only after a second and third inoculation, respectively. In contrast, even following repeated inoculations, Strep. mutans, B. intermedius and Neisseria sp. could not be maintained under glucose-excess conditions. A more extensive pattern of fermentation products and amino acid catabolism occurred under glucose-limited growth; this simultaneous utilization of mixed substrates also contributed to the higher yields (Y molar glucose) and greater species diversity of these communities. Microscopic and biochemical evidence suggested that cell-to-cell interactions and food chains were occurring among community members. To compare the reproductibility of this system, communities were established on three occasions under glucose-limitation and twice under glucose-excess conditions. The bacterial composition of the steady-state communities and their metabolic behaviour were similar when grown under identical conditions but varied in a consistent manner according to the nutrient responsible for limiting growth. Although a direct simulation of the oral cavity was not attempted, the results show that the chemostat could be used as an environmentally-related model to grow complex but reproducible communities of oral bacteria for long periods from a defined inoculum.