Quinolone accumulation by Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli

The accumulation of nalidixic acid and 14 fluoroquinolones over a range of external drug concentrations (10-100 mg/L; c. 25-231 mu M) into intact cell s of Escherichia coli KL-16, Staphylococcus aureus NCTC 8532, Pseudomonas a eruginosa NCTC 10662 and spheroplasts of E. coli was investigated. The effe ct of 100 mu M carbonyl cyanide m-chlorophenyl hydrazone (CCCP) upon the co ncentration of quinolone accumulated by intact cells and spheroplasts of E. coli was also determined. Except for pefloxacin, there was an increase in the concentration of the six quinolones examined accumulated by E. coli, de spite a reduction in fluorescence at alkaline pH. For ciprofloxacin the par tition coefficient (P-app) was constant despite an increase in the pH; howe ver, the P-app far nalidixic acid decreased significantly with an increase in pH. The concentration of nalidixic acid, ciprofloxacin and enrofloxacin accumulated by E. coli and S. aureus increased with an increase in temperat ure up to 40 degrees C and 50 degrees C, respectively. Above these temperat ures the cell viability decreased. With an increase in drug concentration t here was, for intact E. coli and 12/15 agents, and for S. aureus and 10/15 agents, a linear increase in the concentration of drug accumulated. However , for P. aeruginosa and 13/15 agents there was apparent saturation of an ac cumulation pathway. Assuming 100% accumulation into intact cells of E. coli , for 10/14 fluoroquinolones less than or equal to 40% was accumulated by s pheroplasts. CCCP increased the concentration of quinolone accumulated but the increase varied with the agent and the bacterial species. The variation in the effect of CCCP upon accumulation of the different quinolones into E . coli could result from chemical interactions or from different affinities of the proposed efflux transporter for each quinolone. Overall, these data suggest that accumulation of most quinolones into E. coli and S aureus pro ceeds by simple diffusion, but that P. aeruginosa behaves differently.