Studies on the Life and Death of Bacteria

The phenomenon of growth and death of bacteria in ordinary culture media has been studied in considerable detail. The data obtained in such studies show that growth follows a definite course, represented frequently by a curve constructed by plotting the logarithms of the numbers of organisms against time. This logarithmic growth curve has been divided into four main parts: the lag, logarithmic growth, maximum stationary, and death phases. After reaching the maximum stationary phase, the curve is frequently shown tapering off until it meets the abscissa, indicating sterility of the culture in a few days or weeks. However, a few of the more recent writers (Gay, 1936; Topley and Wilson, 1936) have made suppositions to the contrary. Gay states: "It is very probable that many cells may be unable to multiply but are still able to carry on other metabolic functions." He further suggests that "The number of viable organisms may also show repeated irregular increases possibly indicating spurts in multiplication. The long period of slow decline has not been studied as intensively as it probably deserves." During the course of our investigations on factors affecting bacterial growth, certain observations suggested that a closer quantitative examination of death and death rates in bacterial cultures might be desirable. The period of prolonged survival and the probable mechanisms involved proved to be of particular interest.