Hello,

Optical Density can be influenced by factors such as the spectrophotometer you use. I advise you 2 things, 1) instead use the McFarland turidity comparison or if you want to have an exact correspondence of your OD with the number of cells you should draw a curve OD = f(Cell) by taking different bacterial suspensions corresponding to different ODs, then spread on a Petri dish corresponding to each OD then carry out a count, you will thus have a correspondence between the OD and the number of cells.