Transport of nucleic acid bases and nucleosides across the bacterial membrane

Abstract Defects have been found in a colorimetric assay developed by its inventors for determining rapidly and quantitatively whether strains of Escherichia coli are resistant to the lethality of mammalian serum. Results gained with the colorimetric assay on the serum resistance of E. coli strains bearing colicin V plasmids differed from results gained with an assay in which the rate of growth of the bacterial strains in a medium containing rabbit serum was estimated turbidimetrically. The colorimetric assay was intended by its developers to facilitate studies of the genetics of serum resistance in pathogenic bacteria. When used as originally described, the assay is likely to mislead in such studies.