Abstract
Larch (Larix decidua) bark is a sawmill waste, traditionally used for antiseptic, expectorant and dermatological (wound healing, eczema, psoriasis) purposes. In this work, we developed a food-grade dry larch bark extract (LBE) from sawmill by-products using hydro-alcoholic extraction. The antibacterial activity of LBE was evaluated against respiratory-tract pathogens, i.e., Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae, Klebsiella pneumoniae, Pseudomonas aeruginosa and Haemophilus influenza, and it was compared to that of grapefruit seed extract (GSE), a commercially available raw material commonly proposed as antibacterial ingredient for over-the-counter products. Procyanidins (PACs) and other polyphenols contents in LBE were determined by HPLC-FLD-MS and HPLC-DAD-MSn, respectively. The antimicrobial activity of LBE and GSE was assessed using the micro-plate dilution technique in concentration range of 2–200 µg/mL, and the safety of these dosages was assessed in cellular and animal models. LBE showed considerable contents of PACs (15% w/w; especially B-type) and other polyphenols (3.8% w/w), among which the characteristic spiropolyphenols larixinol and epilarixinol were identified, together with the flavonoids isoquercitrin and rutin, already reported as growth inhibitors of different respiratory-tract pathogens. LBE showed higher antimicrobial activity compared to GSE, demonstrated by a growth inhibition range of 10–40% towards five of six strains tested, compared to 10–15% of GSE. These results suggest that LBE may represent a natural and sustainable source of active compounds with antibacterial activity for pharmaceutical and nutraceutical applications.
Highlights
Throughout the 15-day observation period, the weight gain of the animals was within the normal range of variation for this strain
Activity compared to LBE, while at the highest dose grapefruit seed extract (GSE) slightly increased bacterial growth. % of respiratory tract pathogens treated with larch bark extract (LBE; blue bars) and experiments. * p
We reported the antimicrobial activity of a standardized larch bark dry hydro-alcoholic extract against several respiratory-tract pathogens, among whom the commonly diffused S. aureus, K. pneumoniae and P. aeruginosa
Summary
The upper respiratory-tract represents a reservoir of bacterial species that can play protective roles or be potentially pathogenic under certain conditions, and among these latter, Streptococcus pyogenes, Haemophilus influenzae, and Staphylococcus aureus have been reported as the most common, especially in children [7]. The treatment of bacterial infections is becoming increasingly challenging, considering that the unprecedented use of antibiotics is leading to the development of bacterial resistance, with dramatic consequences for human healthcare [8]. This leads to the urgent need to discover and develop novel antibiotics, and natural products could represent valuable sources to this regard
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