In vitro efficacy of bioactive extracts of 15 medicinal plants against ESbetaL-producing multidrug-resistant enteric bacteria

Abstract

Alcoholic crude extracts and some fractions from 15 traditionally used Indian medicinal plants were investigated for their ability to inhibit the growth of extended spectrum beta-lactamases (ESbetaL)-producing multidrug-resistant enteric bacteria. The test bacteria Eschrichia coli and Shigella were resistant to 16-23 antibiotics with intermediate or resistance to beta-lactams (minimum inhibitory concentration (MIC) value range 16-1024 microg/ml). The crude plant extracts demonstrated zone of inhibition in the range of 11-29 mm against one or more test bacteria. On the basis of promising activity, 12 plants were selected to determine their efficacy in terms of MIC, which ranged from 0.64 mg/ml to 10.24 mg/ml. The extracts of Acorus calamus, Hemidesmus indicus, Holarrhena antidysenterica and Plumbago zeylanica demonstrated relatively high activity as compared to other plant extracts and were fractionated into acetone, ethyl acetate and methanol. Acetone fraction in most of the cases exhibited higher potency (low MIC value) as compared to ethyl acetate and methanol fraction. However, in Plumbago zeylanica, ethyl acetate fraction was most active. Synergistic interactions among crude extracts were demonstrated in the 12 different combinations against ESbetaL-producing E. coli (ESbetaL-02). Certain combinations exhibited significant synergy with enlargement of combined inhibition zone size by 5 mm. Interaction of crude extracts with five antibiotics (Tetracycline, ciprofloxacin, nalidixic acid, chloramphenicol and streptomycin) demonstrated synergistic interaction with tetracycline and ciprofloxacin by 10 and 3 plant extracts respectively. Phytochemical analysis and thin layer chromatography (TLC) bioautography of crude extracts showed the presence of alkaloids, phenols and flavonoids as active phytoconstituents. Most active fractions of four plants were subjected to Infrared spectroscopy and the major groups of compounds were detected. The plant extracts were further tested for their in vitro haemolytic activity to sheep erythrocytes and demonstrated no haemolysis at recommended doses. Further activity-guided fractionation of active fractions is needed to isolate and characterize the active principle in order to establish the mode of action against the ESbetaL-producing multidrug-resistant enteric bacteria and the mechanism of synergy.