Lag period: bacteria need to adapt to the environment after entering a new medium environment. During this period, the growth of bacteria was weak and the number of viable bacteria was basically stable. The time of this period is generally between 1-4 hours.
Logarithmic growth period: the number of viable bacteria increases linearly on the growth curve of this period. Bacteria have adapted to the culture medium environment, and the bacteria are vigorous and begin to grow and reproduce at high speed. The number of living bacteria increases rapidly with a stable geometric progression, which can last for several hours to several days (depending on the culture conditions and bacterial production). The morphology, dyeing and biological activity of bacteria in this period are typical.
Stable period: the total number of growing flora in this period is in a flat stage, but the vitality of bacterial population changes greatly. Due to the consumption of nutrients in the culture medium, the accumulation of toxic products, the decline of pH and other unfavorable factors, the reproduction speed of bacteria gradually decreased, and the relative number of bacterial deaths began to increase gradually. At this stage, the number of bacterial proliferation and death is gradually balanced.
Decline period: With the extension of culture time, bacterial reproduction becomes slower and slower, and the number of dead bacteria increases obviously. Physiological and metabolic activities tend to stagnate. The number of viable bacteria is decreasing, which is inversely proportional to the culture time. During this period, bacteria become longer, expand or rot abnormally, and even autolyse, making it difficult to identify their shapes.