2. Oxidative results
Nonfermenting bacteria that metabolize glucose via oxidative metabolism give an oxidative result. This result is indicated by a small amount of acid production in the open tube. The acid produced (pH 6.0) changes the pH indicator, bromthymol blue, from green to yellow (6, 8). After a 24-hour incubation a change in pH is observed at the surface of the open tube where growth in the presence of oxygen is observed (2) (Fig. 2a). With prolonged incubation (more than 48 hours), the reduced concentration of agar in the medium allows for the eventual diffusion of the weak acid throughout the whole tube (Fig. 2c). No color change or reaction occurs in the oil-covered tube.