Determination of Inoculum for Microbiological Testing

IMPORTANT POINTS The following key points are discussed: • Quality control microbiology tests require controlled levels of inocula and require fresh preparations of cells for those inocula • The concentration of cells in a suspension can be estimated by optical density, but this must be confirmed by plate count • The optical density readings against cell mass are specific to the microorganism species • The qualification of these readings must be confirmed after major maintenance to the benchtop spectrophotometer (e.g., after replacement of the bulb).