6) as a function of growth phase of the initial inoculum (log or stationary phase): circles = Log phase cells (τ = 16.8 ± 1.13 min); diamonds = stationary phase cells (τ = 16.8 ± 0.313 SIS3 price min). The experiments represented in Fig. 2 were repeated using mid-log phase-associated cells as described in the Experimental section and we saw qualitatively similar results (Fig. 4). The main graph in Fig. 4 represents 987 OD[t] observations with the calculated values of τ plotted as a function of CI. At CIs > ca. 1,000 CFU mL-1 the average τ was unimodally-distributed with a maximum spread of ca. 17
to 22 min (159 observations; μτ ± στ = 17.9 ± 0.645 min). Similar to the stationary phase-based BMS-907351 in vivo cells, we see that as CI was decreased (CI ≤ 200 CFU mL-1 or ≤ 54 ± 7.3 CFU/well), a striking increase occurred in the scatter of τ (spread between 12 and 36 min). The frequency of occurrence of all log phase-based τ values (CI < 1,000 CFU mL-1) are displayed in the inset graph of Fig. 4 (α ~ 0.35; μτ1 ± στ1 = 18.2 ± 0.660 min; β ~ 0.65; μτ2 ± στ1 = 20.0 ± 2.11 min). Figure 4 Plot of 987 observations of τ as a function of initial cell concentration (C I ; diluted log phase E. coli cells). Inset Figure: Frequency of occurrence of various values of τ (C I < 1000 CFU mL -1 ) fit to Eq. 7. It is important to keep in mind throughout this work that by the time we begin to observe an increase in OD (and therefore measure
τ
via Eq. 1), somewhere between 2 and 20 science doublings will have occurred. This fact implies that the values we observe are somehow modulated based upon initial conditions. It should also be noted that low bacterial CIs (i.e., ≤ 5 CFU mL-1) would result in at least some single CFU occurrences per well (i.e., the average probability of observing 1 CFU per well should be about 32.0 ± 6.65%) at which point the first few events of cell division could modulate characteristics of both τ and true microbiological lag time (T). Thus, some of the increase in τ and T scatter we observe at low CI could result from the random selection of isolates with particularly slow growth rates which would otherwise be masked by other isolates in the media with faster rates. However, arguing against such a stochastically-based explanation is the fact that a significant fraction of the scatter in τ (Figs. 2 and 4) occurs between CI = 10-100 CFU mL-1 whereupon the probability of observing 1 CFU per well only ranges from 18.1 to ca. 0%. Under these conditions the random selection of one particular τ-component would be overwhelmed by the sheer number of other cells present. At slightly higher concentrations (e.g., 2 or 3 CFUs per well), any well which has 2 or 3 cells with τ values differing more than about 4 or 5 min would be obvious in the ∂OD[t]/∂t curves as additional peaks. Nevertheless, we just don’t observe such behavior at these low CIs.