Antimicrobial activity of subinhibitory concentrations of aminoglycosides against pseudomonas aeruginosa as determined by the killing-curve method and the postantibiotic effect

This investigation used the postantibiotic effect (PAE) and killing curves to provide data on the antimicrobial activity of subinhibitory (l/8×, 1/4 × and l/2× minimum inhibitory concentration; MIC) and inhibitory (1 × MIC) concentrations of amikacin, gentamicin and tobramycin against Pseudomonas aeruginosa. Subinhibitory concentrations (l/4× and l/2× MIC) of aminoglycosides demonstrated a reproducible PAE. At l/4× MIC, the order of duration of the PAE was approximately 15 min for all aminoglycosides, while at l/2× MIC all three aminoglycosides displayed a similar PAE of approximately 40 min. Killing-curve studies demonstrated that subinhibitory concentrations of aminoglycosides either decrease bacterial growth for several hours (l/4× and l/2× MIC) or produce stasis of growth for several hours (1/8 × MIC). Only inhibitory aminoglycoside concentrations (1 × MIC) proved to be bactericidal. Subinhibitory concentrations of aminoglycosides decrease bacterial growth and produce a PAE against P. aeruginosa.