Quantifying live bacterial densities using non-invasive optical measurements of E. coli

Profiling the growth of bacterial cultures over time can be a tedious and error-prone process. Here, we present the development and evaluation of the use of the ODity platform to optically measure bacterial cell densities non-invasively. The digital growth data for E. coli MG1655 was calibrated against colony forming units (CFU/mL) obtained by plating on solid media. Diauxic-like shifts of liquid E. coli MG1655 cultures grown at 37{degrees}C in LB media were observed at densities as low as 2.9 x 107 {+/-} 1.2 CFU/mL. The shift occurred at a significantly higher cell density (6.0 x 107 {+/-} 1.2 CFU/mL) when the bacteria were cultured at 31{degrees}C. These shifts were only short lived, 15.2 {+/-} 1.5 and 20.8 {+/-} 1.8 min at 37{degrees}C and 31{degrees}C, respectively, with the previous growth rate restored thereafter. We measured minimum doubling times of 17.0 {+/-} 1.1 and 24.8 {+/-} 0.9 min at 37{degrees}C and 31{degrees}C, respectively. These results demonstrate that the growth and growth rate of bacterial cultures can be accurately determined non-invasively using the ODity device.