FIG 1.

Determination of cell density using flow-cytometric and spectrophotometric methods. A culture of M. smegmatis cells grown overnight was serially diluted in MB7H9 medium, and the diluted samples were subjected to analysis. The number of cells (counts), irrespective of viability, present in a given volume of the sample (2.4 μl) was determined by flow cytometry using a FACS instrument. (A) The counts obtained (expressed as counts ml⁻¹) were plotted against relative concentration (conc.). (B) A similar approach was taken for investigating the correspondence between relative concentration and OD₆₀₀. (C) To determine the degree of correspondence between counts obtained by FACS and OD₆₀₀, the respective values were plotted against each other and subjected to linear regression analysis. The goodness of fit is indicated by the R² value. (D to F) Time-dependent changes in the OD₆₀₀ (D), counts ml⁻¹ (FACS analysis) (E), and viable counts (CFU) (F) following the addition of phage (MOI of 1). Error bars represent standard deviations from the means derived from three biological replicate experiments.