[Effects of quinolone carboxylic acid derivatives on the ultrastructure of gram-positive and gram-negative bacteria].

The impact of oxolinic acid, pefloxacin and ciprofloxacin on the structure of Staphylococcus aureus, Pseudomonas aeruginosa and Serratia marcescens was studied. The concentration dependent effects were revealed. Comparative estimation of the action of the compounds by the content of normal, dead and changed cells in the cultures showed that ciprofloxacin had advantages. The results of the pefloxacin use were close. The time course of the oxolinic acid effect was analogous whereas the changes in the cells induced by the acid were less pronounced. Investigation of the ultrastructural changes demonstrated that the response of the gram-negative bacteria to the action of the compounds was of one type. There was noted formation of filamentous structures and vacuolized cells at low concentrations and large egg-shaped cells at high concentrations of the compounds. In the gram-positive bacteria there were detected large cells with much thicker cell walls at low concentrations of the compounds while at the high concentrations the cell walls were on the contrary thinner, the cell stiffness was lost and the cells acquired a festoon-like shape. The compounds induced significant changes in the nucleoids, cell walls and membranes. Along with insignificant changes in the nucleoid structure there were constantly detected coarse impairments of the cell walls and membranes which should be considered in estimating the effect of the quinolone carboxylic acid derivatives.