A simple and widely applicable method for preparing homogeneous and stable quality control samples in water microbiology

Quick freezing in dry ice-ethanol and storage at -70 degrees Celsius of test strains suspended in skim milk yield samples that can be used for quality control. A comparison of counts of selective and nonselective media to evaluate the performance of the strains revealed that the samples can be used immediately after being produced since they are stable, though they require a quick thawing in a water bath at 37 degrees Celsius.