An Interpretation of Bacterial Growth-rate Curves.

THE usual graphical method of expressing the increase of bacterial growth rate in a media by means of the bacterial number/time curve, has several disadvantages, inasmuch as that the maximum growth rate cannot be accurately determined, nor the period of optimum propagation. An improved method of presenting a bacterial growth-rate curve and eliminating the aforementioned disadvantages will now be described, and the new types of curves illustrated. A need for this new method was felt while working on the new photoelectric method of interpreting growth rate by density measurements. A perfect growth rate curve indicating bacterial increase in numbers per time of incubation usually evolves a sigmoid logarithmic curve, neglecting precipitation, death of bacterial organisms, etc. This curve, while indicating the total number of organisms at any given time, fails in not accurately indicating the period of incubation at which the organisms are most rapidly propagating. For all kinds of bacterial organisms the sigmoid curve is usually evaluated, while the new type of curve is comparatively distinctive, approximately indicating by the shape of the curve, the organism; the initial amount of inoculum also introduces an alteration in the shape of the curve. Furthermore, the new curve admirably indicates the period at which the maximum expansion rate takes place in a bacterial colony. The new curve can easily be obtained from any sigmoid curve giving number/time of organisms or dN colony size/time of colonies, by utilising the formula -jfor each period of time