Biochemical test
One colony from the incubated Endo agar plate was prepared according to the provided instructions with 0.9% NaCl solution instead of the 0.85% listed. The analytic tests were then performed according to instructions. The species determination was completed using the chemical test results and a computer database.
Cell counting with Bürker chamber
The method was carried out as per lab instructions, except for the following parts where oral instructions from the lab assistants differed from the written manual. 5 μl instead of 10μl of diluted cell suspension was placed in the chamber and counting was performed only on two 16 square grids and the procedure was not repeated.
The reference concentration was calculated from the provided optical density (OD) of 1 with the conversion factor 1OD = \(3\cdot10^7\)cells/100mL.
The original cell suspension was diluted in a ration of 1:10, giving a volume fraction \(fr_V\)of 0.1.
For a given number of cells per square \(n\), the concentration of cells in the diluted suspension \(C_d\) was then calculated according to (\ref{cd}) and the concentration of cells in the original cell suspension \(C_o\) according to (\ref{co}). Where \(V_s\) denotes the liquid volume of a square.