06 Control LB (L) 0.35 18.2 ± 0.660 0.65 20.0 ± 2.11 1.79 17.9 ± 0.645 Conditioned LB (L) 0.31 19.1 ± 0.627 0.69 20.1 ± 2.10 0.994 18.9 ± 0.700
Sonicated, Heat-killed Cells in LB (L) 0.54 21.0 ± 0.690 0.46 21.3 ± 2.58 0.300 21.1 ± 0.646 Figure 6 Frequency of occurrence of various values of τ (all C I ; C I > 100; C I < 100 CFU mL -1 , from top to bottom). Left-hand side plots: stationary phase cells diluted with and grown in sterile-filtered 'conditioned' LB. Right-hand side plots: stationary phase cells diluted with and grown in LB. Figure 7 A: Frequency of occurrence of various values of τ (all C I ; C I > 100; C I < 100 CFU mL -1 , from top to bottom). Left-hand side plots: mid-log phase cells diluted www.selleckchem.com/products/gsk2126458.html with and grown in LB with ~2×105 CFU mL-1 of disrupted cells LB. Right-hand side plots: mid-Log phase cells diluted with and grown in LB. B: Plot of 572 observations of τ as a function of initial cell concentration (C I ; diluted with and grown in LB with ~ 2×10 5 CFU mL -1 of
disrupted E. coli cells LB). Conclusion Working with a native, food-borne E. coli isolate grown in either LB or MM, we found that microplate-based doubling times were bimodally distributed at low cell densities using either log or stationary phase cells as an initial inoculum. Qualitatively identical PI3K inhibitor selleck screening library results were obtained for an E. coli O157:H7 and Citrobacter strain. When sterile-filtered ‘conditioned’ LB media (formerly contained relatively low concentrations of bacteria or sonicated/heat-killed cells) were employed as a diluent, there were apparent shifts in the two (narrow and broad) populations but the bimodal effect was still evident. However, the bimodal response was almost completely reversed when the growth media contained a small amount of ethyl acetate.
The clear doubling time-cell concentration dependency shown in these results might indicate that bacteria exude a labile biochemical which controls τ, or a need for cell-to-cell physical contact. The latter proposal seems unlikely inasmuch as the probability of random contact would be small at such low cell densities (CI ~ 100-1,000 CFU mL-1). Perhaps this anomalous bimodal distribution of doubling times is related to the recently proposed phenotypic switching [14, 15] which Beta adrenergic receptor kinase describes programmed variability in certain bacterial populations. Methods General Escherichia coli (non-pathogenic chicken isolate) , E. coli O157:H7 (CDC isolate B1409), and Citrobacter freundii (non-pathogenic poultry isolate; identification based on 16 S rDNA analysis)  were cultured using LB (Difco) or MM (60 mM K2HPO4, 33 mM KH2PO4, 8 mM (NH4)2SO4, 2 mM C6H5O7Na3 [Na Citrate], 550 μM MgSO4, 14 μM C12H18Cl2Na4OS [Thiamine•HCl], 12 mM C6H12O6 [glucose], pH 6.8). Liquid cultures were incubated with shaking (200 RPM) at 37°C for ca. 2-4 (for log phase cultures) or 18 hrs (stationary phase cultures) using either LB or MM.