Figure 2.

Population decay during antibiotic treatment shows Syn3B persistence

(A) A simplified model of population decay having two phases: short-term tolerance phase and long-term tolerance phase. Both phases contain heterogeneous populations. The short-term tolerant phase contains susceptible cells, slow-growing cells, transient tolerant cells, persister and viable but nonculturable cells (VBNCs). Transient tolerant cells survive longer than fast-growing susceptible cells, while transient tolerant cells die quicker than the persisters and VBNCs (VBNCs and persisters were not distinguished in this study). The long-term tolerant phase contains both persisters and VBNCs.

(B) Population decay of Syn3B (parent strain). Overnight cultures of Syn3B (parent strain) were grown to stationary phase, diluted to 1:10, and then treated with streptomycin (100 μg/mL) or ciprofloxacin (1 μg/mL) and sampled over time. Error bars represent SEM (n ≥ 3).

(C and D) Population decay of Syn3B P026. Syn3B P026 cells were treated with streptomycin (100 μg/mL) or ciprofloxacin (1 μg/mL) and sampled over time. (C) Stationary phase cells were diluted 1:10 into fresh media containing antibiotics. Error bars represent SEM (n ≥ 6). (D) Exponential phase cells were treated with streptomycin (100 μg/mL) or ciprofloxacin (1 μg/mL) and sampled over time. Error bars represent SEM (n ≥ 3). There is 100% survival at time zero because percent survival is determined by the surviving CFU/ml compared to the CFU/ml at time zero.