Amplification of phleomycin induced death and DNA breakdown by caffeine in escherichia coli

Summary

Caffeine enhanced the degradation of DNA to acid soluble fragments in cultures of Escherichia coli exposed to Phleomycin (≦2 μg/ml). Enhancement was particularly striking with stationary phase cultures, which normally exhibit negligible DNA breakdown when treated with ≦2 μg/ml of Phleomycin. There is little DNA breakdown or death in UVR strains treated with phleomycin (≦2 μg/ml) during exponential growth but when caffeine was present as well as Phleomycin, the kinetics of DNA breakdown and the amounts of DNA degraded were identical in all cultures tested including those of UVR, EXR, B/r type and B strains and equal to the maximum rate observed (with an EXR strain) in the absence of caffeine (ca. 1.7 % per min). High concentrations of Phleomycin (≧10 μg/ml) had the same effect as the caffeine+Phleomycin (≦2 μg/ml) combination and produced a uniform pattern of DNA breakdown in all strains tested. Caffeine did not seem to increase permeability of the bacterial coat. Given to the cells before exposure to Phleomycin it was ineffective in enhancing DNA breakdown. On the other hand, exposure of the bacteria to Phleomycin for a period of ≧40 min at 37° followed by caffeine was as effective as adding the two drugs together.

Caffeine increased the efficiency of Phleomycin as an antibiotic for both growing and stationary phase cultures of e. coli B. It is suggested that caffeine aids the cooperative denaturation of DNA initiated by the attachment of Phleomycin molecules to thymine bases. This would allow single strand-specific endonucleases to attack the DNA and initiate DNA breakdown and cell death.