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

McKee, A.S., McDermid, A.S., Ellwood, D.C. & Marsh, P.D. The establishment of reproducible, complex communities of oral bacteria in the chemostat using defined inocula. Journal of Applied Bacteriology59, 263–275. Nine commonly isolated oral bacterial populations were inoculated into a glucose‐limited and a glucose‐excess (ammo 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 repro‐ductibility 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.