Antibacterial activity of herbal extracts towards uropathogenic Enterococcus isolates as a natural approach in control of urinary tract infections

Abstract

Antibacterial and antibiofilm efficacy through a synergistic effect of herbal leaf extracts of bearberry (BE), bearberry tea (BTE), parsley (PE), and the strawberry tree (STE) was evaluated to discover an alternative approach to control urinary tract infections caused by Enterococci. UHPLC–DAD MS/MS analysis indicated that herbal extracts were rich in ellagic and gallic acids, catechin, quercetin, and arbutin, which are strong antioxidants. Mostly, Enterococcus faecalis isolates showed resistance only to gentamicin and/or norfloxacin (26.3 %) and moderate biofilm production (31.5 %), while 12 isolates of Enterococcus faecium showed multiple antibiotic resistance. The minimum inhibitory concentration for the majority of isolates was 1.25 mg ml−1 for STE, but 2.5 mg ml−1 for BE and BTE. Although individual extracts gave higher MIC values, for most isolates, a synergistic effect at lower concentrations was achieved, when BE or BTE (0.625 mg ml−1) was combined with STE (0.31 mg ml−1). The BTE extract was shown to have the strongest individual effect on initial adhesiveness and on biofilm formation to all selected isolates, while the synergism of BTE and STE caused significant biofilm inhibition at all concentrations tested. The synergistic effect achieved of the tested extract combinations might be a starting point in the development of alternative products, effective against antibiotic resistant Enterococcus isolates.