The antimicrobial activity of tea tree oil nanoliposomes against Escherichia coli

The antimicrobial activity of tea tree oil nanoliposomes against Escherichia coli

Although antibiotics are used as feed additives to combat various bacterial infectious diseases in animals, the continuous emergence of drug-resistant bacterial strains has limited their effectiveness. Since plant essential oils have shown significant antibacterial activity, they have been considered a potential candidate for alleviating the problem of antibiotic resistance.

Lernen: Teebaumöl-Nanoliposomen: Optimierung, Charakterisierung und antibakterielle Aktivität gegen Escherichia coli in vitro und in vivo. Bildquelle: ronstik/Shutterstock

In a recent Poultry Science In this study, researchers formulated tea tree oil nanoliposomes (TTONL) and analyzed their antibacterial effectiveness against pathogenic Escherichia coli (E. coli), which significantly affects the poultry industry. The main aim of the current study is to develop a new drug to promote sustainable and healthy animal husbandry in China.

E. coli infection in poultry

Although most E. coli strains are nonpathogenic and occur naturally in the intestine, some virulent strains can cause Crohn's disease, gastroenteritis, and hemorrhagic colitis. Additionally, pathogenic E. coli cause colibacillosis, a systemic or localized infection commonly seen in poultry. Colibacillosis has also been associated with multiple organ lesions such as air sacculitis, perihepatitis and peritonitis, resulting in significant mortality in poultry.

The cell wall of E. coli is composed primarily of lipopolysaccharide (LPS), and cellular lysis of this bacterium causes a massive release of LPS, which triggers an inflammatory response. In this context, NLRP3 was found to play an important role in inducing an inflammatory response during E. coli infection. Another factor that mediates late-stage inflammation is HMGB1.

Tea tree oil (TTO) and nanoliposomes

TTO is an essential oil extracted from the leaves of the tea tree. This essential oil has a light yellow to clear color and a fresh camphor smell. Typically the tea tree is found on the coast from southern Queensland to northern New South Wales, Australia.

TTO has many medicinal uses including the treatment of herpes, acne, scabies, insect bites and microbial skin infections. Importantly, this essential oil has demonstrated a minimum inhibitory concentration (MIC) of less than 1% against most bacteria and fungi. Therefore, TTO is considered a promising antimicrobial agent.

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Terpinen-4-ol and α-terpineol are the main components of TTO, which promote antibacterial activity. Mechanistically, the bactericidal action of these components has been linked to disruption of the microbial cell membrane, causing cell lysis.

In addition to its advantages, some of the limitations that limit the application of TTO include its insolubility in water, its unstable nature, and the strong tendency of its active ingredients to change when exposed to air. These shortcomings could be overcome by using nanoliposomes, a two-layer vesicle carrier system formed by self-assembly in aqueous media.

Nanoliposomes carrying essential oil reach the target site through cellular interactions (e.g., phagocytosis, adsorption, and fusion). Importantly, these have significantly improved the poor stability of essential oils during storage and use. In this study, TTONL was optimally produced to inhibit E. coli disease in poultry.

Synthesis and characterization of TTONL

TTONL was synthesized using thin film hydration and sonication technique. The development process was optimized using the Box-Behnken Response Surface method. The optimal conditions determined for TTONL synthesis were a lecithin to cholesterol mass ratio of 3.7:1, a hydration medium pH of 7.4, and a TTO concentration of 0.5. These conditions result in a TTONL encapsulation rate of 80.31 ± 0.56%.

Transmission electron microscopy (TEM) analysis showed that TTONL was nearly spherical and uniform in size. The average particle size of this bilayer structure containing TTO was 227.8 ± 25.3 nm with a negative charge. The characteristic absorption peak of TTONL showed an insignificant modification of the basic skeleton of a liposome. Importantly, experimental results showed that TTONL was more stable for 35 days at 4 °C than at room temperature.

Antibacterial effectiveness of TTONL

The antibacterial activity of TTONL was evaluated against E. coli through in vitro and in vivo experiments. For the in vivo study, the effectiveness of TTONL was examined in chickens infected with colibacillosis.

The results of the MIC test showed that the nanoliposomes improved the antibacterial effectiveness of TTO against various E. coli strains. After 8 hours of treatment with 75 mg/ml TTONL, complete bactericidal activity was observed against the test strains.

In vitro experiments showed that TTONL exposure caused varying degrees of structural damage to the E. coli strains. An in vivo study found that oral administration of TTONL significantly reduced clinical symptoms and intestinal lesions in infected chickens. Importantly, TTONL treatment significantly reduced the mRNA expression of NLRP3 and NF-κB in the cecum and duodenum of E. coli-infected chickens.

Conclusions

The newly synthesized TTONL showed higher encapsulation rate, slower release and improved stability with promising antibacterial activity against the tested pathogens. Taking all experimental results into account, the current study strongly recommended the prophylactic use of TTONL for the treatment of avian bacterial diseases.

Reference:

• Bo, R. et al. (2023) „Teebaumöl-Nanoliposomen: Optimierung, Charakterisierung und antibakterielle Aktivität gegen Escherichia coli in vitro und in vivo“, Poultry Science, 102(1), p. 102238. doi: 10.1016/j.psj.2022.102238. https://www.sciencedirect.com/science/article/pii/S003257912200534X?via%3Dihub

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