Synergism between Salvia officinalis extract and antibiotics against human pathogenic bacteria

Abstract

Salvia officinalis L. (Lamiaceae) is a known aromatic and medicinal plant that is in widespread use (antioxidant, anti-inflammatory, antimicrobial, hypoglycemic, anti-mutagenic). A potential herb-drug interaction, which could be beneficial (synergistic interaction), is considered as an alternative approach to treat bacterial infection [1–3]. The aim of this study was to test the antibacterial activity of ethanol extract obtained from leaves of S. officinalis in combination with three commercial antibiotics (chloramphenicol, amoxicillin, doxycycline) and to evaluate a possible synergistic action against ten human pathogenic bacteria. The following bacteria were used: Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 and clinical isolates Staphylococcus aureus, Bacillus subtilis, Enterobacter cloacae, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli and Proteus sp. Before the synergism assays were evaluated, minimal inhibitory concentrations (MICs) of ethanol extract and antibiotics were determined by tube dilution method. The combination effects between extract and antibiotics were studied using checkerboard method and were interpreted according to fractional inhibitory concentration (FIC) index. The synergism was observed, FIC indices were in range from 0.5 to 0.06. Ethanol extract with amoxicillin showed synergy against 8 tested bacteria while with chloramphenicol or doxycycline in relation to 5 tested bacteria. The synergistic effects did not confirm against E. coli and E. coli ATCC 25922. The present study showed that S. officinalis ethanol extract enhanced the antibacterial effects of tested antibiotics against certain bacteria, MIC values of antibiotics were reduced up to 6-times (range: 1/4 to 1/32MIC) while MIC values of extract were reduced up to 10-times (range: 1/4 to 1/128 MIC) and that ethanol extract tested alone was effective at higher concentrations (MIC=5–40mg/ml).