Effect of light on the Lactobacillus casei icrobiological assay.

Because of the considerable differences in the reported values for serum folate in normal subjects using Lactobacillus casei as assay organism the effect of daylight when preparing media for this assay was studied. It was found that the growth properties of the medium were destroyed by direct sunlight and impaired by bright reflected sunlight, therefore reducing the sensitivity of the assay. Adequate precautions regarding exposure to light must be taken.