Lysine Decarboxylase Activity as a Factor of Fluoroquinolone Resistance in Escherichia coli

摘要

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 as 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.