Role of polyamines in reducing the outer membrane permeability of Escherichia coli to antibiotics

Various hydrophilic antibiotics enter the cells of gram-negative bacteria through porin channels, which can be blocked by polyamine cadaverine. In this paper, we studied the rate of porin-mediated transport and the intracellular concentration of the main biogenic polyamines of Escherichia coli cells subjected to fluoroquinolone antibiotics depending on the exposure time. Porin permeability sharply decreased in the first two hours of antibiotic exposure, after that the transport rate continued to decline, but at a lower rate. Free polyamines accumulated by the second hour of the exposure, then putrescine and spermidine declined, and the concentration of cadaverine continued to grow. Activation of micF gene, a product of which is involved in the negative control of ompF porin gene expression, was observed after the two hours of antibiotic exposure. It could be supposed that the inhibition of porin-mediated transport of antibiotics by blocking pores precedes the mechanisms regulating the number of porins. The paper discusses the probable specialization of polyamines in the regulation of porin-mediated transport of antibiotics.