Bacterial Growth Curve

Lag phase

• no measurable increase in bacterial population

• bacteria adapt to new media and resources

• increased metabolic activity, possible increase in cell mass and volume

• changes in gene regulation occur

• most poorly understood phase

• duration varies by species and factors like media composition, temperature, and inoculum size

exponential (log) phase

• rapid increase in bacterial population

• bacteria are healthiest during this phase

• best stage to extract samples for inoculating fresh cultures

• generation time can be calculated by measuring viable cells at regular intervals

stationary phase

• occurs because growth cannot continue indefinitely in a closed system

• resources become limited, space decreases, or toxic byproducts accumulate

• overall growth rate becomes negligible

• difficult to accurately count population due to mix of viable and dying cells

• some bacteria produce antibiotics or form spores during this phase

death/decline phase

• resources depleted or overcrowding harms cells

• bacteria die at an exponential rate

• mirrors exponential phase but in decline

• cells from this phase often cannot establish new cultures, even when transferred to fresh media