Following the introduction of a microbe to a new environment -- such as E.coli in a wound, Salmonella in a sandwich, Streptococcus in a cow's udder, or algae in an aquarium -- the microbe does not increase rapidly as the microbe "adjusts" to the new environmnet. During this lag phase, the number of new cells increases very slowly (reproductions > deaths). Depending on the microbe the lag phase may be several minutes to a few hours or days. In our population study of yeast in a culture tube, it appears that sometimes the lag phase is 2-7 days. Then the microbes begin to double rapidly, and the log phase shows rapid increase in the number of microbes. The log phase or exponential phase has great R> D (reproductions > deaths). The rate of growth is influenced by the genetics of the microbe and the environmental conditions. Procaryotes grow faster than eucaryotes; and small eucaryotes grow faster than larger ones.

Following the log phase is the stationary phase when there is no net increase or decrease in cell number (R = D). Some microbes die and some reproduce balancing each other. It is thought that some microbes have genes that slow down the reproduction rate during the stationary phase. In some populations, the microbes will deplete the available nutrients or release toxins that cause the death of the microbes. This population decline phase is usually gradual and may extend for many weeks or months. In the human infection cycle, it is important that our immune-syetem or the prescribed medication shorten the decline phase as much as possible so that recovery is complete.

The population growth depends on the biotic potential of the microbe. What is the generation time and number of offspring produced? The population growth also depends on the community potential. How much space and nutrients are available? Most of us have observed rapid algae blooms in our aquaria or even small ponds, and we have witnessed the rapid onset of cold symptoms related to the viruses in our body. Microbes do grow rapidly under optimum growth conditions.