Synergistic effects of unripe raspberry extracts (Rubus chingii) and antibiotics against three bacteria

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 (PRE) macroporous resin. Synergistic effects between the URE (or PRE) ampicillin, erythromycin, tetracycline or streptomycin against Escherichia coli, Staphylococcus aureus Salmonella enterica carried out using checkerboard microdilution time-kill curves, respectively. The results showed that all pairwise combinations revealed synergistic effects, with 0.10 ? fractional inhibitory concentration index 0.50 more than 2 × log10 reduction colony-forming units/mL. In particular, erythromycin was reduced to 1/50-1/100 its dose alone while retaining effectiveness S. E. coli. extracts four antibiotics three bacteria related abundance polyphenols extracts, especially ellagic acid. may be dietary supplement and/or natural antimicrobials.