Efficacy of neutral and negatively charged liposome-loaded gentamicin on planktonic bacteria and biofilm communities.

We investigated the efficacy of liposomal gentamicin formulations of different surface charges against Pseudomonas aeruginosa and Klebsiella oxytoca. The liposomal gentamicin formulations were prepared by the dehydration-rehydration method, and their sizes and zeta potential were measured. Gentamicin encapsulation efficiency inside the liposomal formulations was determined by microbiologic assay, and stability of the formulations in biologic fluid was evaluated for a period of 48 h. The minimum inhibitory concentration and the minimum bactericidal concentration were determined, and the in vitro time kill studies of the free form of gentamicin and liposomal gentamicin formulations were performed. The activities of liposomal gentamicin in preventing and reducing biofilm-forming P. aeruginosa and K. oxytoca were compared to those of free antibiotic. The sizes of the liposomal formulations ranged from 625 to 806.6 nm in diameter, with the zeta potential ranging from -0.22 to -31.7 mV. Gentamicin encapsulation efficiency inside the liposomal formulation ranged from 1.8% to 43.6%. The liposomes retained >60% of their gentamicin content during the 48 h time period. The minimum inhibitory concentration of neutral formulation was lower than that of free gentamicin (0.25 versus 1 mg/L for P. aeruginosa and 0.5 versus 1 mg/L for K. oxytoca). The negatively charged formulation exhibited the same bacteriostatic concentration as that of free gentamicin. The minimum bactericidal concentration of neutral liposomes on planktonic bacterial culture was twofold lower than that of free gentamicin, whereas the negatively charged formulations were comparable to free gentamicin. The killing time curve values for the neutral negatively charged formulation against planktonic P. aeruginosa and K. oxytoca were better than those of free gentamicin. Furthermore, liposomal formulations prevent the biofilm-formation ability of these strains better than free gentamicin. In summary, liposomal formulations could be an effective lipid nanoparticle to combat acute infections where planktonic bacteria are predominant.

Antimicrobial properties of liposomal azithromycin for Pseudomonas infections in cystic fibrosis patients.

OBJECTIVES: This work was carried out to construct a novel liposomal azithromycin formulation and examine its antimicrobial effects against Pseudomonas aeruginosa. METHODS: The liposomal azithromycin formulation was prepared by the dehydration-rehydration vesicle method and its characterizations were tested. The MIC and the MBC of the liposomal formulation were determined by the microbroth dilution method. Liposomal azithromycin activity against biofilm-forming P. aeruginosa was assessed using a Calgary biofilm device. The effect of subinhibitory concentrations of liposomal azithromycin on bacterial virulence factors and motility studies was tested on P. aeruginosa strains. The bacteria and liposome interactions were studied using flow cytometry analysis. The toxicities of the liposomal formulation on erythrocytes and A549 lung cells were evaluated in vitro. RESULTS: The average diameter of the liposomal azithromycin was 406.07 ±â€Š45 nm and the encapsulation efficiency was 23.8% ±â€Š0.2%. The MIC and MBC values of liposomal azithromycin were significantly lower than those of free azithromycin. The liposomal azithromycin significantly reduced the bacteria in the biofilm and attenuated the production of different virulence factors; it also reduced the different patterns of bacterial motilities. By flow cytometry analysis data, it was shown that there are interactions of liposomes with the bacterial membranes. No significant haemolysis or cell toxicity was observed with the liposomal formulation. CONCLUSIONS: The results of this research indicate that this novel liposomal azithromycin formulation could be a useful therapy to enhance the safety and efficacy of azithromycin against P. aeruginosa-infected persons.

Liposomal antibiotics for the treatment of infectious diseases.

INTRODUCTION: Liposomal delivery systems have been utilized in developing effective therapeutics against cancer and targeting microorganisms in and out of host cells and within biofilm community. The most attractive feature of liposome-based drugs are enhancing therapeutic index of the new or existing drugs while minimizing their adverse effects. AREAS COVERED: This communication provides an overview on several aspects of liposomal antibiotics including the most widely used preparation techniques for encapsulating different agents and the most important characteristic parameters applied for examining shape, size and stability of the spherical vesicles. In addition, the routes of administration, liposome-cell interactions and host parameters affecting the biodistribution of liposomes are highlighted. EXPERT OPINION: Liposomes are safe and suitable for delivery of variety of molecules and drugs in biomedical research and medicine. They are known to improve the therapeutic index of encapsulated agents and reduce drug toxicity. Recent studies on liposomal formulation of chemotherapeutic and bioactive agents and their targeted delivery show liposomal antibiotics potential in the treatment of microbial infections.

Efficacy and safety of liposomal clarithromycin and its effect on Pseudomonas aeruginosa virulence factors.

We investigated the efficacy and safety of liposomal clarithromycin formulations with different surface charges against clinical isolates of Pseudomonas aeruginosa from the lungs of cystic fibrosis (CF) patients. The liposomal clarithromycin formulations were prepared by the dehydration-rehydration method, and their sizes were measured using the dynamic-light-scattering technique. Encapsulation efficiency was determined by microbiological assay, and the stabilities of the formulations in biological fluid were evaluated for a period of 48 h. The MICs and minimum bactericidal concentrations (MBCs) of free and liposomal formulations were determined with P. aeruginosa strains isolated from CF patients. Liposomal clarithromycin activity against biofilm-forming P. aeruginosa was compared to that of free antibiotic using the Calgary Biofilm Device (CBD). The effects of subinhibitory concentrations of free and liposomal clarithromycin on bacterial virulence factors and motility on agar were investigated on clinical isolates of P. aeruginosa. The cytotoxicities of the liposome preparations and free drug were evaluated on a pulmonary epithelial cell line (A549). The average diameter of the formulations was >222 nm, with encapsulation efficiencies ranging from 5.7% to 30.4%. The liposomes retained more than 70% of their drug content during the 48-h time period. The highly resistant strains of P. aeruginosa became susceptible to liposome-encapsulated clarithromycin (MIC, 256 mg/liter versus 8 mg/liter; P < 0.001). Liposomal clarithromycin reduced the bacterial growth within the biofilm by 3 to 4 log units (P < 0.001), significantly attenuated virulence factor production, and reduced bacterial twitching, swarming, and swimming motilities. The clarithromycin-entrapped liposomes were less cytotoxic than the free drug (P < 0.001). These data indicate that our novel formulations could be a useful strategy to enhance the efficacy of clarithromycin against resistant P. aeruginosa strains that commonly affect individuals with cystic fibrosis.

Efficacy of liposomal bismuth-ethanedithiol-loaded tobramycin after intratracheal administration in rats with pulmonary Pseudomonas aeruginosa infection.

We sought to investigate alterations in quorum-sensing signal molecule N-acyl homoserine lactone secretion and in the release of Pseudomonas aeruginosa virulence factors, as well as the in vivo antimicrobial activity of bismuth-ethanedithiol incorporated into a liposome-loaded tobramycin formulation (LipoBiEDT-TOB) administered to rats chronically infected with P. aeruginosa. The quorum-sensing signal molecule N-acyl homoserine lactone was monitored by using a biosensor organism. P. aeruginosa virulence factors were assessed spectrophotometrically. An agar beads model of chronic Pseudomonas lung infection in rats was used to evaluate the efficacy of the liposomal formulation in the reduction of bacterial count. The levels of active tobramycin in the lungs and the kidneys were evaluated by microbiological assay. LipoBiEDT-TOB was effective in disrupting both quorum-sensing signal molecules N-3-oxo-dodeccanoylhomoserine lactone and N-butanoylhomoserine lactone, as well as significantly (P < 0.05) reducing lipase, chitinase, and protease production. At 24 h after 3 treatments, the CFU counts in lungs of animals treated with LipoBiEDT-TOB were of 3 log(10) CFU/lung, comparated to 7.4 and 4.7 log(10) CFU/lung, respectively, in untreated lungs and in lungs treated with free antibiotic. The antibiotic concentration after the last dose of LipoBiEDT-TOB was 25.1 µg/lung, while no tobramycin was detected in the kidneys. As for the free antibiotic, we found 6.5 µg/kidney but could not detect any tobramycin in the lungs. Taken together, LipoBiEDT-TOB reduced the production of quorum-sensing molecules and virulence factors and could highly improve the management of chronic pulmonary infection in cystic fibrosis patients.