Antibacterial and plasmid curing activity of lomefloxacin in vitro

The in vitro activity of lomefloxacin in comparison to other recently developed quinolones was evaluated by determination of MICs for 89 test strains. Organisms tested included clinical isolates of gram-positive and gram-negative bacteria susceptible or resistant to quinolones, resistant mutants of Enterobacteriaceae, Pseudomonas aeruginosa, Staphylococcus aureus and Enterococcus faecalis obtained in vitro, and the wild type strain Escherichia coli K12 with its mutants na1A, nalB, nalC and nalB. The activity of lomefloxacin was similar to that of pefloxacin against gram-positive cocci and similar to that of norfloxacin against gram-negative bacteria. There was cross-resistance to all quinolones tested in pefloxacin resistant clinical isolates and in laboratory mutants. The activity of lomefloxacin was decreased against the Escherichia coli K12 mutants nalA and nalD but not nalB, whereas the nalC mutant showed increased susceptibility. Susceptible and mutant strains (n = 115) were used to establish the least-squares lines of regression with 5-micrograms and 10-micrograms lomefloxacin disks. Tests of the in vitro plasmid curing activity of lomefloxacin compared to other agents showed no statistically significant plasmid loss after treatment with lomefloxacin.