Abstract
Abstract Dried unripe raspberries (Rubus chingii), a kind of Chinese herbal medicine, have been used for many years in China. They were prepared as unpurified raspberry extract (URE) by ethanol extraction, and purified raspberry extract (PRE) by macroporous resin. Synergistic effects between the URE (or the PRE) and ampicillin, erythromycin, tetracycline or streptomycin against Escherichia coli, Staphylococcus aureus and Salmonella enterica were carried out using checkerboard microdilution and time-kill curves, respectively. The results showed that all pairwise combinations revealed synergistic effects, with 0.10 ≤ fractional inhibitory concentration index ≤ 0.50 and more than 2 × log10 reduction in colony-forming units/mL. In particular, the erythromycin concentration in the combinations was reduced to 1/50-1/100 of its dose alone while retaining its effectiveness against S. aureus and E. coli. The synergistic effects of raspberry extracts and four antibiotics against three bacteria were related to the abundance of polyphenols in the extracts, especially ellagic acid. The extracts may be a dietary supplement and/or natural antimicrobials.
Highlights
The unripe raspberry of Rubus chingii Hu, containing high medicinal ingredients e.g. polyphenols, terpenoids, saponins, polysaccharides, alkaloids, and essential oils, exhibits antioxidant, anti-bacteria, anti-complement and anticancer activities (Yang et al, 2019; Yu et al, 2019)
The Realgar-Indigo naturalis formula (RIF) based on 100,000 Traditional Chinese Medicine formulae is very effective in treating human acute promyelocytic leukemia
Their minimal inhibitory concentration (MIC) against Escherichia coli, Staphylococcus aureus and Salmonella enterica ranged from 2-20 mg/mL (Yang et al, 2019)
Summary
The unripe (green) raspberry of Rubus chingii Hu, containing high medicinal ingredients e.g. polyphenols, terpenoids, saponins, polysaccharides, alkaloids, and essential oils, exhibits antioxidant, anti-bacteria, anti-complement and anticancer activities (Yang et al, 2019; Yu et al, 2019). It is the only plant of Rubus species included in The Chinese Pharmacopoeia and used to improve kidney functions, such as enuresis and urinary frequency, in Traditional Chinese Medicine for many years (Chinese Pharmacopoeia Commission, 2015). Their MICs against Escherichia coli, Staphylococcus aureus and Salmonella enterica ranged from 2-20 mg/mL (Yang et al, 2019)
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