Each cell in the dish divides once it accumulates enough biomass, following logistic growth: division slows as the colony approaches the dish's carrying capacity K. Antibiotic dose lowers the effective growth rate and adds a stochastic kill term per bacterium, mimicking bactericidal action.
dN/dt = r_eff · N · (1 − N/K) − k_kill(a) · N
r_eff = r0 · (1 − a/100)
k_kill(a) = 0.15 · (a/100)
t_double = ln(2) / r_eff
Releasing phages seeds free bacteriophage particles that random-walk toward the nearest uninfected cell. On contact the phage injects its genome (infection); after a fixed latent period the cell lyses, releasing a burst of ~8 new phage progeny — the classic lytic cycle.
- Growth rate r₀ — sets the baseline logistic division speed of the colony.
- Antibiotic dose — reduces effective growth and adds a per-cell death probability each second.
- Release phages — seeds bacteriophage particles that hunt, infect, and lyse bacteria.
- Reset dish — reseeds the petri dish with a fresh starter colony.
This mirrors real clinical logic: antibiotic susceptibility testing tracks how dose changes doubling time, while phage therapy exploits the lytic cycle as an alternative to antibiotics against resistant bacteria.