DNA-protective effect of polyamines as the factor of Escherichia coli levofloxacin resistance

Effect of natural polyamines on susceptibility of Escherichia coli clinical isolates to fluoroquinolone antibiotic levofloxacin was studied. Objects: E. coli clinical isolates of different fluoroquinolone resistance level (sensitive, intermediate and resistant). Methods: estimation of antibiotic minimal inhibitory concentration by the standard 2fold dilution antimicrobial susceptibility test; registration of DNA damage by agarose gel electrophoresis of pDNA samples extracted out of E. coli cells exposed to antibiotics and polyamines; determination of hydroxyl radicals with 3'-(hydroxyphenyl) fluorescein cell staining followed by fluorescent detection with microplate reader. We found that putrescine and spermidine, but not cadaverine, increased significantly the resistance of E. coli clinical isolates with different susceptibility to levofloxacin in a concentration-dependent manner. Antibiotic activity of levofloxacin was accompanied by promotion of reactive oxygen species formation and DNA damage in bacterial cells. When added to antibiotic-treated cells, polyamines putrescine and spermidine reduced the in-tracellular production of reactive oxygen species and prevented DNA damage. Thereby, it was found that poly-amines putrescine and spermidine decrease the susceptibility of E. coli isolates to fluoroquinolone antibiotic levofloxacin through, in particular, their antioxidant activity.