Melaleuca armillaris nanoencapsulated against methicillin resistant Staphylococcus aureus

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

Brujas

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

European Association for Veterinary Pharmacology and Toxicology

Introduction: Bovine mastitis is one of the main pathologies that affect dairy cattle, is an infectious disease with a high impact on public health and milk industry profitability. Staphylococcus aureus causes intramammary infections in dairy cows. Its pathogenesis and antimicrobial resistance make it necessary to find alternative treatments, being the nanoencapsulation of essential oils (EO) very promising. Materials and Methods: Nanostructured lipid carriers (NLC) containing 5% of Melaleuca armillaris EO were prepared. Physicochemical characteristics such as particle size (mean diameter and size distribution were measured by photon correlation spectroscopy), loading efficiency and release of EO during 72 h (measuring EO concentrations at 230 nm using a UV–Vis spectrophotometer) were evaluated. Also, antimicrobials properties against S. aureus (resistant -N = 3 -and sensible -N = 4 –to methicillin) were analyzed, establishing minimum inhibitory and bactericidal concentrations (MIC and MBC, respectively) and minimum inhibitory concentrations of biofilm formation and eradication (MICB50 and MECB50, respectively). Finally, cytotoxicity of EO free and nanoencapsulated on neutrophils during 6 h of exposure at concentrations of 10–0.05 μL/mL was evaluated. Results: Mean size of NLC-EO was 190 nm and did not change after 6 months storage at 4 °C. Encapsulation efficiency of EO in NLC was 71.5%. NLC containing EO showed a biphasic release behavior with a fast initial release during the first 6 h, followed by a slow release afterwards, releasing 60% of the EO in 72 h. The EO controlled release profiles remained for at least 72 h. The EO (free and nanoencapsulated) 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 to the unexposed control). The MECB50 was 12.5 μL/mL and 0.3 μL/mL for the nanoencapsulated EO and for free EO, respectively, against all strains assayed. Empty NLCs inhibited biofilm formation, but not planktonic growth or eradicated preformed biofilms. The free EO was cytotoxic for neutrophils, however, the encapsulation of EO in NLC decreased its cytotoxicity, with cell viability being 70% after 6 h for 0.05 μL/mL of EO and 32% for 10 μL/mL.Conclusions: The EO was efficiently encapsulated and released in NLC, and was highly antimicrobial against MRSA and SASM, both in planktonic culture and in biofilm. Viability of neutrophils was higher by encapsulating the EO, an important factor for future experimentsevaluating intracellular activity of EO, where S. aureus survives and evades the action of poorly penetrating antibiotics.