Effects of ethylenediaminetetraacetic acid and gentamicin on the antibacterial activity of pyridone carboxylic acid derivatives against gram-negative bacilli

Abstract

Ofloxacin (9-fluoro-3-methyl-10-(4-methyl-1-piperazynyl)-7-oxo-2,3-dihydro-7 H-pyrido-(1,2,3-de)1,4-benzoxazine-6-carboxylic acid) and enoxacin (1-ethyl-6-fluoro-1,4-dehydro-4-oxo-7-(1-piperazinyl)-1, 8-naphthyridine-3-carboxylic acid) are newly developed pyridone carboxylic acid derivatives with broad and potent antibacterial activities against Gram-negative and Gram-positive bacteria. Antibacterial activities of six pyridone carboxylic acid derivatives, including these two new antibiotics, were examined against Gram-negative bacilli in the presence and absence of ethylenediaminetetraacetic acid (EDTA) or gentamicin. The minimal inhibitory concentrations (MICs) of nalidixic acid, cinoxacin and piromidic acid were reduced by the addition of EDTA or gentamicin. However, the MICs of pipemidic acid, ofloxacin and enoxacin were unaffected. These findings indicated the high permeability of pipemidic acid, ofloxacin and enoxacin through the outer membrane. The effects of EDTA and gentamicin against Serratia marcescens were different from those against other Gram-negative bacilli.