Lysine decarboxylase activity as a factor of fluoroquinolone resistance in Escherichia coli

Abstract

Exposure of E. coli cells to sublethal concentrations of fluoroquinolones induced synthesis of lysine decarboxylase LdcC, which was previously considered to be a constitutive enzyme. Under these conditions, a key role in this process is played by RNA polymerase σS subunit (RpoS); its quantity increased substantially in the presence of antibiotics. Fluoroquinolones of the second and third generations had a more pronounced effect on rpoS expression and LdcC activity than the first-generation antibiotics. A direct correlation was shown between the level of cadaverine, the product of lysine decarboxylase reaction in E. coli cells, and their resistance to fluoroquinolones. An increase in endogenous cadaverine reduced effectiveness of the second and third-generation fluoroquinolones, but had no effect on antimicrobial activity of the first-generation antibiotics. This is in good agreement with the hydrophilic properties of antibiotics of different generations and, consequently, with different mechanisms of their penetration into bacterial cells.