Characterisation and in vitro antimicrobial potential of liposome encapsulated silver ions against Candida albicans.

Liposomes are biocompatible, biodegradable, controlled delivery systems with the ability to encapsulate both lipophilic and hydrophilic compounds, including metal ions. Liposome encapsulated Ag(+) (lipo-Ag(+)), prepared by reverse-phase evaporation, was used as a controlled delivery system against Candida albicans. Characterisation of the lipo-Ag(+) indicated that the multilamellar vesicles with diameters ranging between ≈ 0.5 and 5.0 µm showed potential as a controlled delivery system to consistently deliver Ag(+) to C. albicans. Results from inductively coupled plasma (ICP) analysis showed higher association of cell bound Ag(+) at 15 mins post exposure when compared to unencapsulated Ag(+). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicate detrimental effects of Ag(+) on C. albicans cell structure. These effects along with the ICP results also correlate with previously reported time kill experiment observations.

Ionically Crosslinked Chitosan Hydrogels for the Controlled Release of Antimicrobial Essential Oils and Metal Ions for Wound Management Applications.

The emerging problems posed by antibiotic resistance complicate the treatment regime required for wound infections and are driving the need to develop more effective methods of wound management. There is growing interest in the use of alternative, broad spectrum, pre-antibiotic antimicrobial agents such as essential oils (e.g., tea tree oil, TTO) and metal ions (e.g., silver, Ag⁺). Both TTO and Ag⁺ have broad spectrum antimicrobial activity and act on multiple target sites, hence reducing the likelihood of developing resistance. Combining such agents with responsive, controlled release delivery systems such as hydrogels may enhance microbiocidal activity and promote wound healing. The advantages of using chitosan to formulate the hydrogels include its biocompatible, mucoadhesive and controlled release properties. In this study, hydrogels loaded with TTO and Ag⁺ exhibited antimicrobial activity against P. aeruginosa, S. aureus and C. albicans. Combining TTO and Ag⁺ into the hydrogel further improved antimicrobial activity by lowering the effective concentrations required, respectively. This has obvious advantages for reducing the potential toxic effects on the healthy tissues surrounding the wound. These studies highlight the feasibility of delivering lower effective concentrations of antimicrobial agents such as TTO and Ag⁺ in ionically crosslinked chitosan hydrogels to treat common wound-infecting pathogens.

Antimicrobial efficacy of liposome-encapsulated silver ions and tea tree oil against Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans.

UNLABELLED: The activity of alternative antimicrobial agents such as tea tree oil (TTO) and silver ions (Ag(+) ) with multiple target sites impedes the development of antibacterial resistance and might be useful in improving the current treatment strategies for various chronic wound infections. In this study, liposome-encapsulated TTO, Ag(+) and TTO plus Ag(+) were added to suspension cultures of Pseudomonas aeruginosa (Ps. aeruginosa), Staphylococcus aureus (Staph. aureus) and Candida albicans (C. albicans). Treatment of these cultures using the agents in combination at subminimal lethal concentrations resulted in an enhanced loss of viability compared to treatment with individual agents. The effective concentration, elimination time (to the limit of detection, LOD) and fractional lethal concentration index (FLCI) of liposomal agents in combination were as follows: Candida albicans: 0·05% v/v TTO:PVA30-70 kDa : 8·9 × 10(-5) % w/v Ag(+) :PVA30-70 kDa : 2·0 h, FLCI = 0·73 (indifferent), Staphylococcus aureus: 0·05% v/v TTO:PVA30-70 kDa : 6·0 × 10(-4) % w/v Ag(+) :PVA30-70 kDa : 1·5 h, FLCI = 0·38 (synergistic), Pseudomonas aeruginosa: 0·25% v/v TTO:PVA30-70 kDa : 3·2 × 10(-4) % w/v Ag(+) :PVA30-70 kDa : 30 min, FLCI = 0·33 (synergistic). These results show the potential for improving antimicrobial efficacy by delivering lower effective concentrations of alternative agents, via controlled release systems. NB All values denoted as %w/vAg(+) refer to the concentration of silver ions. SIGNIFICANCE AND IMPACT OF THE STUDY: In this study, we have shown that encapsulating silver (as the ion Ag(+) ) and tea tree oil (singly and in combination) in a controlled release liposomal carrier system can improve their antimicrobial efficacy as well as reduce the effective concentration required. These findings may impact on the problems of agent toxicity caused by the need for high effective doses or microbial resistance where long term application is required.

Antimicrobial efficacy of silver ions in combination with tea tree oil against Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans.

Tea tree oil (TTO) and silver ions (Ag(+)), either alone or in combination with other antimicrobial compounds, have been used in the treatment of topical infections. However, there appears to be little data on the efficacy of TTO combined with silver in the absence of any other agents. TTO and Ag(+) were added, alone and in combination, to suspension cultures of Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans. Treatment of these cultures with TTO and Ag(+) at sub-minimal lethal concentrations resulted in an enhanced loss of viability compared with treatment with individual agents. The order of sensitivity to the combined agents was P. aeruginosa>S. aureus>C. albicans. The fractional lethal concentration index (FLCI) showed that these combinations of TTO and Ag(+) exerted a synergistic effect against P. aeruginosa (FLCI=0.263) and an indifferent effect against S. aureus and C. albicans (FLCI=0.663 and 1.197, respectively). The results indicate that combining these antimicrobial agents may be useful in decreasing the concentration of antimicrobial agents required to achieve an effective reduction in opportunistic pathogenic microorganisms that typically infect wounds.

Antimicrobial action and efficiency of silver-loaded zeolite X.

AIMS: To synthesize silver-loaded zeolite X and establish the extent to which it persist in its antimicrobial action against strains of Escherichia coli K12W-T, Pseudomonas aeruginosa NCIMB8295 and Staphylococcus aureus NCIMB6571. METHODS AND RESULTS: The antimicrobial action and efficacy of silver-loaded zeolite X on Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa were investigated. Zeolite X was synthesized and loaded with Ag(+) by ion exchange. This resulted in 2.0% (w/w) loading of Ag(+) in the zeolite framework and 5.8% (w/w) on the zeolite. Escherichia coli and Pseudomonas aeruginosa and Staphylococcus aureus suspended in tryptone soya broth were exposed to 0.15, 0.25, 0.5 or 1.0 g l(-1) of silver-loaded zeolite X for a period up to 24 h. No viable cells were detected for any of the three micro-organisms within 1 h. Silver-loaded zeolite X, retrieved three times from the first exposure cultures, was washed with de-ionized water and added to fresh bacterial suspensions. The results showed that the silver-loaded zeolite X retained its antimicrobial action. CONCLUSIONS: Silver-loaded zeolite X persisted in its antimicrobial action against all three micro-organisms. SIGNIFICANCE AND IMPACT OF THE STUDY: The results are significant for the longevity of antimicrobial action of silver-loaded zeolite X.

Bacterial synthesis of biodegradable polyhydroxyalkanoates.

Various bacterial species accumulate intracellular polyhydroxyalkanoates (PHAs) granules as energy and carbon reserves inside their cells. PHAs are biodegradable, environmentally friendly and biocompatible thermoplastics. Varying in toughness and flexibility, depending on their formulation, they can be used in various ways similar to many nonbiodegradable petrochemical plastics currently in use. They can be used either in pure form or as additives to oil-derived plastics such as polyethylene. However, these bioplastics are currently far more expensive than petrochemically based plastics and are therefore used mostly in applications that conventional plastics cannot perform, such as medical applications. PHAs are immunologically inert and are only slowly degraded in human tissue, which means they can be used as devices inside the body. Recent research has focused on the use of alternative substrates, novel extraction methods, genetically enhanced species and mixed cultures with a view to make PHAs more commercially attractive.

Effect of hyperbaric oxyhelium gas on response of bacteria to antimicrobial agents in vitro.

Modern diving techniques can require the treatment of infection in an atmosphere of pressurized oxyhelium gas. The antibiotic susceptibility of 16 species and strains (eight genera) of gram-negative bacilli and 3 species and strains (two genera) of gram-positive cocci to each of 21 antimicrobial agents was assessed in air at atmospheric pressure and in oxyhelium gas at an absolute pressure of 7 bar (ca. 709 kPa). A disk diffusion technique was employed, and significantly different results were obtained in the two atmospheres. The effect of oxyhelium on diameters of growth inhibition varied significantly with the bacterium and with the antibiotic and was particularly marked with certain bacterium-antibiotic combinations. The gram-negative bacilli generally gave reduced zone diameters in oxyhelium, whereas the gram-positive cocci showed a mixture of effects.

Effects of hyperbaric oxygen on the growth and properties of Pseudomonas aeruginosa.

Growth of Pseudomonas aeruginosa in 2 atmospheres absolute of 100% oxygen at 37 degrees C produced two types of abnormal colonies--stunted, rough colonies, termed dwarfs, and large, domed, mucoid colonies, termed giants. The occurrence of these variants depended upon the partial pressure of oxygen and the inoculum size. Subculture of dwarf or giant colonies produced a mixture of both colony types after incubation in hyperbaric oxygen, and colonies of normal appearance after incubation in air. Electron micrographs of ultrathin sections showed that cells from dwarf colonies had a more clearly defined envelope region than cells from normal colonies. Giant colony and normal colony-derived cells were of similar appearance. Whole cells from giant colonies contained more carbohydrate, readily extractable lipid, neutral lipid and free fatty acid than cells from normal colonies; the two cell types showed similar contents of 2-keto,3-deoxyoctonic acid and total phospholipid, but different proportions of individual phospholipids. Cells from dwarf, giant and normal (air-grown) colonies were incubated in air on nutrient agar containing either polymyxin, tetracycline or phenoxyethanol. Relative to cells from normal colonies, cells from dwarf colonies showed enhanced resistance to all three agents and cells from giant colonies showed enhanced resistance to polymyxin and tetracycline only. The resistance of cells from variant colonies was lost following a single subculture in air in the absence of antibacterial agents. It was concluded that the envelopes of cells from dwarf and giant colonies differed both from each other and from those of normal cells. These differences, and the formation of variant colonies, appeared to result from bacterial adaptation to hyperbaric oxygen rather than from mutation.

Influence of R-plasmid RP1 of Pseudomonas aeruginosa on cell wall composition, drug resistance, and sensitivity to cold shock.

R-plasmid RP1 was transferred to Pseudomonas aeruginosa cells, as indicated by their resistance to carbenicillin, ampicillin, cephaloridine, kanamycin, and tetracycline, and by the presence of a periplasmic beta-lactamase. The wild-type cells (RP1-) were lysed by ethylenediaminetetraacetic acid but not by ethylene-glycol-bis(2-aminoethyl ether)-N,N-tetraacetic acid, whereas cells carrying the plasmid (RP1+) were resistant to both these chelating agents. RP1+ and RP1- strains were both sensitive to the lytic action of polymyxin B and the lethal action of cold shock, but the effect was less marked in the RP1+ cultures. A proportion of the RP1+ cells surviving cold shock lost resistance to carbenicillin, tetracycline, and kanamycin. The chemical composition of whole cells and cell walls of RP1+ differed from that RP1- in the content of cation, phospholipid, and markers for lipopolysaccharide and peptidoglycan. Differences in cell wall composition, response to ethylenediaminetetraacetic acid and polymyxin B, and the effects of cold shock are all compatible with the hypothesis that RP1 confers changes in the cell envelope, probably in the outer membrane, of P. aeruginosa.