Biochemical test

One colony was taken from the incubated Endo agar plate, the preparation of which is described in the MPN method section above and dissolved in 5ml 0.9% NaCl solution. This solution was used to prepare an Analytical profile index (API) test according to provided instructions as well as standard biochemical tests for bacterial motility (Motility test), presence of gram-negative, lactcto-fermenting bacteria (MacConkey test), bacterial oxidation (OF-O test) and bacterial fermentation (OF-F test). These tests were incubated for 24 hours and the results analysed using a computer database.

Cell counting with Bürker chamber

The method was carried out as per lab instructions, except for three parts where oral instructions from the lab assistants differed from the written manual. Firstly, only 5 μl of the diluted cell suspension was put in the chamber.  Secondly, the yeast cells were not counted until a limit of 100-150 had been identified, instead the number of cells per square was counted for two 16 square grids. Thirdly, the counting procedure was only repeated for two grids. In instances where mother and daughter cells were stuck together two and two, they were counted as one. Clusters of several mother and daughter cells were counted as one or two, depending on total amount of cells in cluster. The optical density (OD) of the undiluted yeast solution was 1, accoutring to oral information from the lab assistants.
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 \(C_d\) can then be 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.