Evaluation of colony‐forming ability experiments using normal and DNA repair‐deficient human fibroblast strains and an automatic colony counter

An automated procedure for evaluation of colony-forming ability experiments has been developed using normal and xeroderma pigmentosum fibroblast strains. Technically this consists of an image analyzer equipped with a contrast-intensifying video camera, monitor, and a desk-top computer. Complex structures composed of overlapping colonies could be reduced to the constituent single colonies by special correction programs. Eighteen experiments were evaluated, and the D0 values for colony-forming ability were determined. A systematic but correctable deviation between visual and automated counting was found. The source of this deviation is described and a solution for correction is provided. The automatic procedure reduced the evaluating time by a factor of five to ten.