Melaleuca armillaris nanoencapsulated against methicillinresistant Staphylococcus aureus

BULDAIN, DANIEL; ISLAN GA; GORTARI CASTILLO, LIHUEL; MARCHETTI, LAURA; MESTORINO, NORA

Congreso; 15th International Congress of the European Association for Veterinary Pharmacology and Toxicology; 2023

European Association for Veterinary

Introduction: Bovine mastitis is one of the main pathologies that af-fect dairy cattle, is an infectious disease with a high impact on publichealth and milk industry profitability. Staphylococcus aureus causesintramammary infections in dairy cows. Its pathogenesis and antimi-crobial resistance make it necessary to find alternative treatments,being the nanoencapsulation of essential oils (EO) very promising.Materials and Methods: Nanostructured lipid carriers (NLC) contain-ing 5% of Melaleuca armillaris EO were prepared. Physicochemicalcharacteristics such as particle size (mean diameter and size distribu-tion were measured by photon correlation spectroscopy), loading ef-ficiency and release of EO during 72 h (measuring EO concentrationsat 230 nm using a UV–Vis spectrophotometer) were evaluated. Also,antimicrobials properties against S. aureus (resistant - N = 3 - andsensible - N = 4 – to methicillin) were analyzed, establishing minimuminhibitory and bactericidal concentrations (MIC and MBC, respec-tively) and minimum inhibitory concentrations of biofilm formationand eradication (MICB50 and MECB50 , respectively). Finally, cytotox-icity of EO free and nanoencapsulated on neutrophils during 6 h ofexposure at concentrations of 10–0.05 μL/mL was evaluated.Results: Mean size of NLC-EO was 190 nm and did not change after6 months storage at 4 °C. Encapsulation efficiency of EO in NLC was71.5%. NLC containing EO showed a biphasic release behavior witha fast initial release during the first 6 h, followed by a slow releaseafterwards, releasing 60% of the EO in 72 h. The EO controlled re-lease profiles remained for at least 72 h. The EO (free and nanoen-capsulated) had a MIC of 6.25 μL/mL for all the strains; however,with 0.3 μL/mL biofilm formation was inhibited (90% with respect tothe unexposed control). The MECB50 was 12.5 μL/mL and 0.3 μL/mLfor the nanoencapsulated EO and for free EO, respectively, againstall strains assayed. Empty NLCs inhibited biofilm formation, but notplanktonic growth or eradicated preformed biofilms. The free EOwas cytotoxic for neutrophils, however, the encapsulation of EO inNLC decreased its cytotoxicity, with cell viability being 70% after 6 hfor 0.05 μL/mL of EO and 32% for 10 μL/mL.Conclusions: The EO was efficiently encapsulated and released inNLC, and was highly antimicrobial against MRSA and SASM, both inplanktonic culture and in biofilm. Viability of neutrophils was higherby encapsulating the EO, an important factor for future experimentsevaluating intracellular activity of EO, where S. aureus survives andevades the action of poorly penetrating antibiotics