Adaptive functions of Escherichia coli polyamines in response to sublethal concentrations of antibiotics

Abstract

Escherichia coli exposure to sublethal antibiotic concentrations induced an increase in cell polyamine contents. Maximum accumulation of putrescine and spermidine in response to antibiotics-induced oxidative stress preceded the increment of cadaverine, the content of which was dependent on the rpoS expression level and reached the maximum in response to fluoroquinolones. The polyamine positive modulating effects on rpoS expression increased in the following order: cadaverine-putrescine-spermidine. The reason for cadaverine accumulation was the increase in activities of lysine decarboxylases CadA and Ldc. High cadaverine accumulation in the cells exposed to fluoroquinolones and cephalosporins resulted in the reduction of porin permeability; so it was considered as a response aimed at cell protection against antibiotic penetration into the cell. Netilmycin, unlike other antibiotics, did not substantially affect the lysine decarboxylase activity and cellular polyamine pools.