Anti-staphylococcal activity in vitro and in vivo of essential oil of Baccharis salicifolia

DANIELA ECHENIQUE; OLGA ALIENDRO; HUGO CENTORBI; XIOMARA GAMBLUCH; CLAUDIA MATTANA; CLAUDIA AGUILERA MERLO; ALBANA CRUCEÑO; ALEJANDRO A. ORDEN; SARA SATORRES

Lima

Congreso; XXX Congreso Peruano de Química - XXX Congreso Italo-Latinoamericano de Etnomedicina; 2023

SILAE - Sociedad Italo-Latinoamericana de Etnomedicina y SQP - Sociedad Química del Perú

Staphylococcus aureus is a Gram-positive bacterium that colonizes the skin and mucous membranes of humans, being the anterior nostrils the main reservoir, from where it can spread and be responsible for a wide spectrum of diseases. Its resistance to multiple antibiotics makes it necessary to search for new therapeutic options. Baccharis salicifolia (R. & P.) Pers. (Asteraceae), popularly known as «Chilca amarga» or «jarilla de río» is a shrub native to the Province of San Luis, Argentina. This plant is used in folk medicine as a diuretic, digestive, and liver protector agent. The influence of this bacterium in the presence and absence of essential oil of B. salicifolia on nasal carriage was studied in a mouse model. The antibacterial activity of the essential oil was tested against methicillin-resistant S. aureus (MRSA) strain ATCC 43300. The oil was obtained from the aerial parts of B. salicifolia and isolated by hydrodistillation. The minimum inhibitory concentration (MIC)  was assayed using microplate method in tripticase soya broth supplemented with 0.01 % (w/v) of 2,3,5-triphenyltetrazolium chloride as visual indicator of bacterial growth. Subcultures on tripticase soya agar were performed to evaluate the minimal bactericidal concentration (MBC).The experiments were performed in duplicate. For the nasal infection model, three consecutive days of procedures were followed. On the first day, BALB/c mice were intranasally inoculated with 1x108 CFU/mL of MRSA. On the second day, half of the mice received a nasal administration of the essential oil of B. salicifolia at a concentration of 500 μg/mL, while the other half served as a control group. On the third day, all mice were euthanized using cervical dislocation. The nares, spleen, and lung were removed and homogenized for bacterial quantification and histological studies. Uninfected mice were used as controls. The nasal tissues was fixed in Bouin´s solutions for approximately 12-24 hours. Later they were dehydrated in alcohols of increasing concentration and included in paraffin and stained according to the Hematoxylin- Eosin staining technique (H-E). The essential oil of B. salicifolia showed inhibitory activity against S. aureus ATCC 43300 (MIC of 250 µg/ml) and bactericidal activity (MBC of 500 µg/ml). However, the administration of this essential oil into the nostrils of BALB/c mice infected with MRSA did not result in a significant difference in infection as evidenced by a similar bacterial count in their nasal homogenates. In the histological study, mice infected with MRSA showed mucosa with a keratinized flat stratified epithelium without alterations and a lamina propria with a moderate presence of adipose cells. Conversely, mice treated with the essential oil showed some significant morphological changes in the nasal mucosa, with a great development of adipose tissue, altered adipocytes and marked blood vessel dilation. Control mice without infection showed a normal structural organization of the nasal mucosa. The increase in adipocytes would constitute a defense response against S. aureus infection by the host. This study contributes to the discovery of new plants with antibacterial properties and opens a way to the isolation and identification of active principles with antibiotic activity.