SGT values are proportional to the initial inoculum. The linearity of SGT method was assessed in various strains and conditions. (A) Growth curves of the wild-type P. aeruginosa strain PA14 (PA) grown in LB (Green), LB + 3% Ethanol (Yellow) and in the defined medium M63 (Pink); PA14 isogenic mutant derivative cyt b1 (light blue); and wild-type strains A. baumanii (black) and E. coli DH5α (dark blue). (B) The time when the growth curves crossed the threshold (OD600nm = 0.15 - 0.2) is defined as the SGT. P. aeruginosa PA14 cells were grown to OD600nm = 2.0, when the concentration of cells was 4.07 x 109 ± 7.02 x 108 cells/mL according to CFU counts. The cells were diluted serially 1:10 in a 96-well plate reader to ODs below the detection threshold of the spectrophotometer, after which their growth kinetics was recorded and also determined at 18 h by CFU counts. Each growth curve is the average of at least 3 repeats. (C) Plots of SGT values versus bacterial concentrations detected by CFU count reveal linear correlation in all cases (R2 >0.99). Colors of the circles correspond to inoculum concentrations. The linear regression curve is shown in red. (D - E) Growth curves and plots of SGT values versus bacterial concentrations detected by CFU count for the additional conditions and strains.
Hazan et al. BMC Microbiology 2012 12:259 doi:10.1186/1471-2180-12-259