Microbial Growth and Replication
The characteristic four-phase pattern of population growth when bacteria are inoculated into fresh liquid medium.
| Phase | Description |
|---|---|
| Lag phase | Minimal increase in cell number; bacteria are metabolically active, synthesising enzymes and adapting to the new medium, but not yet dividing at maximum rate |
| Log (exponential) phase | Rapid, exponential increase in cell number; each cell divides at a constant interval, the phase of maximum metabolic activity and the target window for most antibiotic action, since many antibiotics require active cell wall synthesis or protein synthesis to exert their effect |
| Stationary phase | Growth rate slows and plateaus as nutrients become depleted and waste products accumulate; rate of new cell division approximately equals rate of cell death |
| Death phase | Viable cell count progressively declines as nutrient exhaustion and toxic waste accumulation exceed the population's capacity to survive |
- This curve is directly relevant to antibiotic pharmacodynamics: beta-lactams, which target active cell wall synthesis, are most effective against rapidly dividing organisms in log phase and comparatively ineffective against dormant or slowly dividing organisms, a key reason some infections (e.g. those involving biofilms or persister cells) are difficult to eradicate with these agents alone.
