Accumulation and killing kinetics of fifteen quinolones for Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa

The accumulation of fifteen quinolone antimicrobial agents (nalidixic acid, eight mono-fluorinated agents, three di-fluorinated agents and three tri-fluorinated agents) by Escherichia coli KL16, Staphylococcus aureus NCTC 8532 and Pseudomonas aeruginosa NCTC 10662 was studied. The concentration of quinolones accumulated varied with the quinolone and the bacterial species, and was not affected by the number of fluorine atoms on the quinolone nucleus. There was also no direct relationship between the hydrophobicity or the molecular size of each drug and accumulation or activity. The killing of the three strains by the fifteen quinolones at a concentration of 10 mg/L was determined in broth and phosphate buffer to mimic the conditions of the accumulation assay. The bactericidal activity varied with the agent and the strain, and usually reflected the in-vitro activity of the drug. Despite most agents causing a decrease in the viable count of the three strains there was no detectable effect on the pattern of accumulation of the quinolones.