Effects of methanolic extract of sour cherry (Prunus cerasus L.) on microbial growth

The antimicrobial activity of a methanolic extract of the common edible fruit Prunus cerasus L. was evaluated. HPLC analysis of the extract revealed the abundant presence of anthocyanins. Minimum Inhibitory Concentrations (MIC) for Gram-positive and Gram-negative pathogenic bacteria was in the range 26.6 mg mL-1, whereas the time-kill assay revealed that the bactericidal effect was exerted only at concentrations higher than 2X MIC. Interestingly, at concentrations lower than MIC, P.similar to cerasus L. extract exerted a stimulating effect on bacterial proliferation and on the ability to form biofilms. In particular, a multidrug-resistant Acinetobacter baumannii strain showed a 30% increase in growth at low concentrations. In the light of this finding, we speculate that the use of berry extracts (rich in anthocyanins) may present some risks to human health when used as preservatives in food and cosmetic products.