Promising antimicrobial activities of oil and silver nanoparticles obtained from Melaleuca alternifolia leaves against selected skin-infecting pathogens

Abstract The leaves of Melaleuca alternifolia contain tea tree oil (TTO), which has been used as a topical antiseptic for decades. The aim of this study was to evaluate the antimicrobial efficacy of TTO from and silver nanoparticles (AgNPs) synthesized in leaf aqueous extract against selected skin-infecting microbes, namely: Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pyogenes, Klebsiella pneumoniae, Pseudomonas aeruginosa, Trichophyton mentagrophytes, Candida albicans, herpes simplex virus type 1 (HSV-1), and herpes simplex virus type 2 (HSV-2). The major oil components characterized by GC/MS analysis were: terpinen-4-ol, limonene, γ-terpinene, α-terpinene, cineol, and α-terpinolene. Characterization of AgNPs by transmission electron microscopy (TEM) showed them to be homogenous and spherical with an average size of 11.56 nm. Bioassay results showed that both TTO and AgNPs possess potent antimicrobial properties against tested strains, producing marked inhibition zones (14.8-24.7 mm). TEM was also used to study the interaction between nanoparticles and bacterial cells, using Staph. aureus as model. TEM photos showed aggregation of AgNPs around and within bacterial cells, with loss of normal cell structure indicating clear biocidal action. Additionally, tests against HSV-1 and HSV-2 showed that AgNPs had the strongest antiviral activity, causing 44.0% and 45.04% reduction of the cytopathic effect for HSV-1 and HSV-2, respectively. In conclusion, TTO and AgNPs possess good antimicrobial activities against the selected skin pathogens, and could provide cheap alternatives for treating related skin infections either as single agents or in the form of nanoemulsion combinations.