A short review on the antimicrobial micro- and nanoparticles loaded with Melaleuca alternifolia essential oil

Determination of antibacterial and anti-biofilm activities of Terpinen-4-ol loaded polydopamine nanoparticles against Staphylococcus aureus isolates from cows with subclinical mastitis

Mastitis in cows is one of the most important diseases that give rise to economic losses in dairy farms. Increasing antimicrobial resistance in Staphylococcus aureus, one of the most common causes of mastitis, is a significant health problem. Due to the problems encountered in treating infections caused by resistant strains, developing alternative treatment methods, such as Nanomaterial systems and natural agents, are important. The essential oil of Melaleuca alternifolia is used as an antibacterial and the primary active component is terpinen-4-ol. This study aimed to investigate the antibacterial and anti-biofilm activity of terpinen-4-ol and terpinen-4-ol loaded polydopamine (T-PDA) nanoparticles against S. aureus isolates, which were resistant to at least one group of antibiotics isolated from milk samples of subclinical mastitis cows. The S. aureus strains were identified by biochemical tests and verified with the API Staph kit. The antibiotic susceptibility of the isolates was determined by the disc diffusion method. The broth microdilution method determined the antimicrobial activities of the terpinen-4-ol and T-PDA nanoparticles, and anti-biofilm activities were assessed using the modified crystal violet method. All of the isolates were resistant to benzylpenicillin and susceptible to trimethoprim/sulfamethoxazole. Multi-antibiotic resistance was detected in the 11 S. aureus isolates used in this study. For the terpinen-4-ol and T-PDA nanoparticles, MIC values were determined in the range of 0.125-0.5% (µL/mL) and 0.125-0.25% (µL/mL), respectively. None of the isolates formed biofilms. As a result, it was found that the antibacterial efficacy of the T- PDA nanoparticles was higher against nine of the S. aureus isolates than against the terpinen-4-ol.

Nanoemulsions and nanocapsules loaded with Melaleuca alternifolia essential oil for sepsis treatment

Sepsis represents a complex clinical syndrome that results from a harmful host response to infection. The infections most associated with sepsis are pneumonia, intra-abdominal infection, and urinary tract infection. Tea tree oil (TTO) has shown high antibacterial activity; however, it exhibits low aqueous solubility and high volatility, which have motivated its nanoencapsulation. In this study, the performance of nanoemulsions (NE) and nanocapsules (NC) loaded with TTO was compared. These systems were prepared by spontaneous emulsification and nanoprecipitation methods, respectively. Poly-ε-caprolactone or Eudragit® RS100 were tested as polymers for NCs whereas Tween® 80 or Pluronic® F68 as surfactants in NE preparation. Pluronic® F68 and Eudragit® RS100 resulted in more homogeneous and stable nanoparticles. In accelerated stability studies at 4 and 25 °C, both colloidal suspensions (NC and NE) were kinetically stable. NCs showed to be more stable to photodegradation and less cytotoxic than NEs. After sepsis induction by the cecal ligation and puncture (CLP) model, both NE and NC reduced neutrophil infiltration into peritoneal lavage (PL) and kidneys. Moreover, the systems increased group thiols in the kidney and lung tissue and reduced bacterial growth in PL. Taken together, both systems showed to be effective against injury induced by sepsis; however, NCs should be prioritized due to advantages in terms of cytotoxicity and physicochemical stability.

Nanoformulated meloxicam and rifampin: inhibiting quorum sensing and biofilm formation in Pseudomonas aeruginosa

Background: We aimed to investigate the simultaneous effects of meloxicam and rifampin nanoformulations with solid lipid nanoparticle (SLN) and nanostructured lipid carrier (NLC) substrates on inhibiting the quorum-sensing system of Pseudomonas aeruginosa and preventing biofilm formation by this bacterium. Methods: Antimicrobial activity of rifampin and meloxicam encapsulated with SLNs and NLCs against P. aeruginosa PAO1 was assessed by disk diffusion, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Results: The SLN formulation was associated with lower doses for the MIC and minimum bactericidal concentration in comparison to NLC. Moreover, our results demonstrated that both nanoformulations were able to produce 100% inhibition of the biofilm formation of P. aeruginosa PAO1. Conclusion: All these findings suggest that meloxicam and rifampin encapsulated with SLNs could be the most effective formulation against P. aeruginosa.

Impact of alginate coating combined with free and nanoencapsulated Carum copticum essential oil on rainbow trout burgers

Carum copticum essential oil (CEO) is known as a valuable active food and pharmaceutical ingredient with antimicrobial and antioxidant activities. Solid lipid nanoparticles incorporated with CEO can overcome their limitations, namely low physicochemical stability and water solubility. In the current study, the antimicrobial and antioxidant activity of free and nanoencapsulated CEO were measured. The results revealed that although the nanoparticles of CEO had higher DPPH radical scavenging activity compared to free CEO, the antimicrobial activity of free CEO toward Escherichia coli and Listeria monocytogenes was higher than nanoparticles. Fish burger samples coated with free and nanoencapsulated CEO and stored for 12 days at 4°C. Alginate coating without CEO was considered as a control sample. The mean zeta potential, particle size, and polydispersity index (PDI) of nanoparticles were 19.18 ± 0.9 mV, 286.5 ± 18.2 nm, and 0.32 ± 0.01, respectively. The results revealed that lipid oxidation, microbial growth, and production of total volatile basic nitrogen in fish burger samples coated with alginate enriched with nanoencapsulated CEO were lower than free CEO. The main volatile compounds of CEO were para-cymene, γ-terpinene, and thymol, which were responsible for the antioxidant and antimicrobial activity of CEO. The data obtained by the current study suggest the application of alginate coating with CEO in form of nanoparticle to enhance fish burgers' shelf life stored at 4°C.

The Assessment of Antimicrobial and Anti-Biofilm Activity of Essential Oils against Staphylococcus aureus Strains

The increase in antimicrobial resistance and tolerance over the years has become a serious public health problem, leading to the inevitable development of alternative antimicrobial agents as substitutes for industrial pharmaceutical antibiotics targeting humans and animals under the concept of one health. Essential oils (EOs) extracted from aromatic and pharmaceutical plants incorporate several bioactive compounds (phytochemicals) that positively affect human and animal health. Herein, this work aimed to examine a standardized chemical composition and screen the antimicrobial and anti-biofilm activity of Thymus sibthorpii, Origanum vulgare, Salvia fruticosa, and Crithmum maritimum EOs against three different Staphylococcus aureus strains by gold-standard disc diffusion, broth microdilution, and microtiter plate biofilm assays. Therefore, the evaluation of the above-mentioned EOs were considered as substitutes for antibiotics to combat the ever-mounting antimicrobial resistance problem. The observed bacterial growth inhibition varied significantly depending on the type and concentration of the antimicrobials. Thymus sibthorpii was determined as the strongest antimicrobial, with 0.091 mg/mL minimum inhibitory concentration (MIC) and a 14-33 mm diameter inhibition zone at 5% (v/v) concentration. All tested EOs indicated almost 95% inhibition of biofilm formation at their half MIC, while gentamicin sulfate did not show sufficient anti-biofilm activity. None of the methicillin-resistant strains showed resistance to the EOs compared to methicillin-sensitive strains. Thymus sibthorpii and Origanum vulgare could be potential alternatives as antimicrobial agents to overcome the problem of microbial resistance. The tested EOs might be incorporated into antimicrobial products as safe and potent antimicrobial and anti-biofilm agents.

Formulation and characterization of propolis and tea tree oil nanoemulsion loaded with clindamycin hydrochloride for wound healing: In-vitro and in-vivo wound healing assessment

This study aimed to develop propolis and tea tree oil nanoemulsion loaded with clindamycin hydrochloride to heal wound effectively. Nanoemulsion formulae were prepared and characterized by droplet size analysis, zeta potential, viscosity, ex-vivo permeation, and skin deposition. The optimal formula was evaluated in terms of morphology, cytotoxicity, and in-vitro wound healing assay. Also, the efficacy of the optimal formula was evaluated by in-vivo wound healing and histopathological studies. The optimal formula (F3) was composed of 9% tea tree oil and 0.4% propolis extracts with mean droplet size 19.42 ± 1.7 nm, zeta potential value −24.5 ± 0.2 mV, and viscosity 69.4 ± 1.8 mP. Furthermore, the optimal formula showed the highest skin deposition value 550.00 ± 4.9 µg/cm² compared to other formulae. The TEM micrograph of the optimal formula showed that the nanoemulsion droplet has an almost spherical shape. Also, the optimal formula did not show noticeable toxicity to the human skin fibroblast cells. The in-vitro and in-vivo wound healing assay showed unexpected results that the un-loaded drug nanoemulsion formula had a comparable wound healing efficacy to the drug-loaded nanoemulsion formula. These results were confirmed with histopathological studies. Our results showed that the propolis and tea tree oil nanoemulsion, whether loaded or unloaded with an antibiotic, is an efficient local therapy for wound healing.

Functionalization of mesoporous silica as an effective composite carrier for essential oils with improved sustained release behavior and long-term antibacterial performance

In this work, a novel composite carrier system for loading essential oils was developed by using tetraethyl orthosilicate (TEOS) and (3-aminopropyl) triethoxysilane (APTES) as silica precursors and cetyl trimethyl ammonium bromide (CTAB) as a template, and the resultant aminated mesoporous silica was further chemically modified by polyacrylic acid (PAA). The obtained composite carriers exhibited a high loading capability toward tea tree oil (TTO), and they also significantly improved the release behavior of TTO due to the steric hindrance of silica mesopore and the polymer restriction. Besides, it was found that the release behavior followed the First-Order kinetic model, revealing that the release of TTO was driven by the concentration gradient. In addition, these composite carriers with essential oil-loaded demonstrated remarkable antibacterial performance againstE. coliandS. aureus, and they could retain antibacterial performance even after 50 d. Moreover, the antibacterial mechanism was also elucidated with the assistance of nucleic acid and conductivity measurements. Therefore, this work provides a facile and environmentally friendly approach to preparing effective composite carriers for improving the sustained release of essential oils, and the long-term antibacterial performance of these essential oil-loaded composite carriers makes them tremendously potential for practical applications.