AN EARLY PHASE IN THE BACTERICIDAL ACTION OF 5-FLUOROURACIL ON E. COLI K 12 . OSMOTIC IMBALANCE

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Abstract
During studies of the action of 5-fluorouracil (FU) on Escherichia coli K-12, the exposed cultures were plated on hyperosmotic nutrient agar plates; close to 95% of the original cells then become viable colony formers; whereas the same percentage fail to give rise to colonies on ordinary nutrient agar. The restoration seems to be a function of the osmotic strength of the , medium, and potassium, sodium or ammonium chlorides, nitrates or sulfates as well as sucrose, maltose, mannose and mannitol were equally effective. The "osmotic restoration" may be related to some interference of FU in the uracil metabolism of the cell. If an aliquot of E. coli K-12 is aerobically incubated with 1 mg/ml FU and an equimolar concentration of uracil for one hour and plated on normal and salt-supplemented agar plates, uracil is found to provide 100% protection against the osmotic imbalance. With thymine as the adjuvant, only 40% of the original population gives rise to viable colonies on normal agar as against 100% on supplemented agar.