Original Article
Cationic amphiphile in phospholipid bilayer or oil–water interface of nanocarriers affects planktonic and biofilm bacteria killing

https://doi.org/10.1016/j.nano.2016.08.011Get rights and content

Abstract

A cationic amphiphile, soyaethyl morpholinium ethosulfate (SME), immobilized in liposomes or nanoemulsions, was prepared in an attempt to compare the antibacterial activity between SME intercalated in the phospholipid bilayer and oil–water interface. Before antibacterial assessment, the size of the liposomes and nanoemulsions was respectively recorded as 75 and 214 nm. The data of minimum inhibitory concentration (MIC)/minimum bactericidal concentration (MBC) and live/dead cell count demonstrated a superior antimicrobial activity of nanoemulsions compared to liposomes against Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), and Staphylococcus epidermidis. Nanoemulsion incubation reduced biofilm thickness by 2.4-fold, whereas liposomes showed a 1.6-fold decrease in thickness. SME insertion in the oil–water phase was found to induce bacterial membrane disruption. SME nanosystems were nontoxic to keratinocytes. In vivo topical application of the cationic nanosystems reduced skin infection, MRSA load, and inflammation in mice. The deteriorated skin barrier function evoked by MRSA was recovered by nanoemulsion treatment.

Graphical Abstract

A cationic amphiphile, soyaethyl morpholinium ethosulfate (SME), immobilized in liposomes or nanoemulsions, was prepared in an attempt to compare the antibacterial activity between SME intercalated in the phospholipid bilayer and oil–water interface. The current study successfully demonstrated the antimicrobial activity of SME loaded in liposomes and nanoemulsions. The lipid-based nanodispersions not only eradicated the planktonic cells but also inhibited biofilm cells. SME immobilized in nanoparticles could adhere to the bacterial surface to disorganize the membrane structure and enhance the permeability, leading to cell death. The antibacterial activity of SME depended on the interfacial intercalation in the nanoparticulate surface.

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Section snippets

Preparation of liposomes

Soy phosphatidylcholine (Phospholipon® 80H, 250 mg) and cholesterol (70 mg) were dissolved in a 5-ml volume of a chloroform: ethanol (2:1) solution. SME (40 mg) was also added in the mixture. The solvent was evaporated in a rotary evaporator at 50 °C, and solvent traces were removed under a vacuum overnight. The phospholipid film was hydrated with double-distilled water (pH = 6.8) using a probe-type sonicator at 35 W for 30 min to form the liposomal dispersion (10 ml). The temperature increased to 45

Physicochemical properties of the nanoparticles

The ingredients of the nanoparticles were plain. Liposomal vesicles were composed of phosphatidylcholine, cholesterol, and SME, while nanoemulsions consisted of sesame oil, water, and SME. The amphiphilic SME could be readily entrapped in the interfacial phospholipid bilayer and oil–water interface of the liposomes and nanoemulsions, respectively. Physicochemical data allowed comparison of the liposomes and nanoemulsions as shown in Table 1. The size of the liposomes and nanoemulsions was found

Discussion

This study compared the antibacterial activity of SME intercalated in interfacial phospholipid bilayers and an oil–water interface. Both lipidic nanosystems were shown to induce bacterial cell membrane damage, suggesting a mechanism for a biocidal effect. Nanoemulsions provided superior germicidal and antibiofilm activity compared to liposomes. The in vivo cutaneous MRSA infection experiment indicated a quick healing of infected abscess by the cationic nanoparticles with no risk of toxicity.

SME

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    There is no disclosure.

    We have no conflict of interest.

    Financial support: The authors are grateful to the financial support of Chi Mei Medical Center (104-CM-FJU-03).

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    Equal contribution.

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