Fig. 3.

Influence of the detectability and growth rate of cells on the accurate determination of growth in dilution cultures beginning with one cell per tube. The signal per cell is 1/N _d, where N _d is the minimum number of cells per tube that can be detected reliably and related to growth (e.g., Table 1). The time required for this detection, t _d (day), is plotted for a range of exponential growth rates. The gray line indicates the observation period for the experiment, t _obs (day)—in this case, 10 days. Points below the line represent combinations of growth rate and cell signal that would lead to reliable detection of growth. Slower growing or less effectively detected cells will register growth if t _obs is increased (raising the gray line); the sensitivity of the detection method is increased (moving points to the right along the curves for each growth rate); or conditions are optimized to increase growth rates (cells move to a lower line)