Isolation and characterization of efflux pump inhibitors of Staphylococcus aureus from medicinal plants of Western Himalayas

Abstract

newline xi newlineABSTRACT The emergence of infections caused by multidrug resistant S. aureus in the hospital and community settings is an increasing health concern. This organism uses different mechanisms of antibiotic resistance, but resistance due to efflux pump has overshadowed by other known mechanisms. In this study, 23 medicinal plant extracts and antibiotics (ciprofloxacin and norfloxacin) were evaluated against three strains of S. aureus (2378 NorA over-expressive, 8325-4 wild type, 1758 NorA knockout) for their synergistic as well as efflux pump inhibitory activity. Methanolic and ethyl acetate extract of Angelica glauca, Dactylorhiza hatagirea, Ficus carica, Girardinia diversifolia, Heracleum lanatum, Malva neglecta, Picrorhiza kurrooa, Rheum australe, Rubia cordifolia, Sedum glaucophylum, Sinopodophylum hexandrum, Solena amplexicaulis, Valeriana jatamansi, Verbascum thapsus and Viola canescens showed synergistic activity with ciprofloxacin and norfloxacin against S. aureus strains by well diffusion method. The maximum synergistic activity with GIIs values of 0.76 and 0.73 was observed for methanolic extract of Heracleum lanatum with ciprofloxacin and norfloxacin respectively. Twelve plant extracts (Angelica glauca (ME), Ficus carica (EE), Heracleum lanatum (ME), Malva neglecta (EE), Picrorrhiza kurrooa (EE), Rheum australe (EE), Sedum glaucophyllum (ME), Sinopodophyllum hexandrum (EE), Solena amplexicaulis (ME), Valeriana jatamansi (ME), Verbascum thapsus (EE), Viola canescens (ME)) showed efflux pump inhibitory activity as measured by berberine uptake assay and EtBr accumulation assay. Maximum efflux pump inhibitory activity was detected in methanolic extract of Angelica glauca and Heracleum lanatum four-fold reduction in the MIC of berberine against 2378 NorA over-expressive and 8325-4 wild type strains of S. aureus. No reduction in the MIC was observed against 1758 NorA knockout strain. Principal phytoconstituents such as carbohydrates, reducing sugars, glycosides, amino acids and proteins, terpenoids, tannins and phenolics, flavonoids and saponins were present in the root extract of Angelica glauca (ME) and Heracleum lanatum (ME). The bioassay guided fractionation of the most bioactive extract from Angelica glauca leads to the isolation of ferulic acid with Rf value of 0.5 and molecular weight of 194.12 as characterized by TLC and LC/MS. Ferulic acid when combined with efflux pump substrates (ciprofloxacin, norfloxacin and cetrimide) resulted in synergistic interaction against 2378 NorA over-expressive and 8325-4 wild type strains of S. aureus. Ciprofloxacin and norfloxacin in combination with ferulic acid showed synergistic effect by reducing the MIC by eight-fold and four-fold respectively against 2378 newlinexii newlineNorA over-expressive strain and 8325-4 wild type strains of S. aureus. Ferulic acid showed synergistic activity with cetrimide by four-fold reduction in the MIC against 2378 NorA over-expressive strain and 8325-4 wild type strains. No interaction was observed in case of 1758 NorA knockout strain. newlineKeywords: multidrug resistance (MDR), S. aureus, efflux pumps, efflux pump inhibitory activity, ferulic acid, cetrimide, NorA, Angelica glauca, Heracleum lanatum, Medicinal plants.