Comparison of the Bactericidal Action of Amikacin, Netilmicin and Tobramycin in Free and Liposomal Formulation against <i>Pseudomonas aeruginosa</i>

Abstract

The rates at which free, cationic and anionic liposomal forms of amikacin, netilmicin and tobramycin kill Pseudomonas aeruginosa were studied in vitro. Control inocula with no antibiotic yielded 6.76, 9.53 and 9.74 log CFU/ml at 0, 6 and 24 h, respectively. Empty anionic or cationic liposomes had no effect on bacterial growth. The killing rates of free antibiotics against the bacterial strain were not enhanced by the addition of either empty anionic or cationic liposomes. After 6 and 24 h of exposure at 1, 2 and 4 times the minimum inhibitory concentrations, free amikacin, netilmicin and tobramycin demonstrated a more rapid bactericidal effect than encapsulated anionic or cationic liposomes. The killing rates of liposomal aminoglycosides were lower than those of free aminoglycosides at identical concentrations, suggesting that only fractions of the encapsulated drugs were released from liposomes.

Antibacterial activity of liposomal gentamicin against Pseudomonas aeruginosa: a time–kill study

“…At 1 × MIC, liposomal and free gentamicin showed a similar pattern, where bacterial growth was inhibited but no noticeable drop in bacterial counts occurred. This result is similar to our previous observation [34], where free tobramycin as well as tobramycin encapsulated in liposomes composed of egg lecithin, stearylamine and cholesterol inhibited bacterial growth but did not reduce the cell counts significantly. Therefore, it appears that low concentrations of these antibiotics are not sufficient to induce significant bacterial death.…”

Mechanism of Enhanced Activity of Liposome-Entrapped Aminoglycosides against Resistant Strains of Pseudomonas aeruginosa

“…Killing curve assays were performed as previously described (28). Briefly, overnight cultures of P. aeruginosa in a final inoculum of 5 ϫ 10 5 /ml were incubated with either free-or liposome-encapsulated antibiotics at one, two, and four times their respective MICs.…”

Enhanced Antibacterial Activity of Echinacea angustifolia Extract against Multidrug-Resistant Klebsiella pneumoniae through Niosome Encapsulation

“…This may increase the fluidity of the bacterial membrane and facilitate the entry of the released extract into the bacterial cell. Moreover, niosomes can increase the stability of the extract, thus providing prolonged activity [58]. The greater penetration of the extract-encapsulated niosome into the bacterial cells can lead to higher bactericidal activities [59].…”