Antibacterials from medicinal plants
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In vitro efficacy of 15 medicinal plant extracts against multi drug resistant enteric bacteria had been reported at our laboratory. The extracts of Acorus calamus, Hemidesmus indicus, Holarrhena antidysenterica, and Plumbago zeylanica demonstrated promising activity as compared to other tested plant extracts. Acetone fractions in most of the cases exhibited high potency as compared to ethyl acetate and ethanol fractions. Some of the extracts showed synergistic interaction with antibacterial drugs, tetracycline and ciprofloxacin. TLC bioautography showed the presence of alkaloids, phenols, and flavonoids as active constituents [55].
4. Anti-MRSA activity of medicinal plants The Anti-MRSA activity has been documented by few workers in certain phytocompounds and plant extracts like Camellia sinensis, Caesalpinia spinosa, Rosa eanina, Scutellara amoena, Arctostaphylos isvaris, Delonix regia, Erytherina variegata, Hypericum spp. etc. [53, 56-61]. Some of the relevant works has been summarized below. The antibacterial activity of phytoalexins, which are biosynthesized by plants and function as self defensive phyto-chemical against microbial infections has been screened based on the phytotherapeutic concept. Potent anti-MRSA activity was found in phytoalexins isolated from Sofora exigna, and these were chemically characterized as hydroxy-flavanones. Lower plants belonging to the leguminosae are abundant in flavonoid phytoalexins, which include flavanone derivatives, structurally analogues to the anti-MRSA flavonones [43, 62, 63]. The substituted flavanones were isolated from leguminous plants and compared their antibacterial activity against methicillin resistant S. aureus (MRSA). Among the thirteen flavanones tested, tetrahydroxy flavanones with these structural characteristics, isolated from Sofora exigna and Echinosphora koreensis showed activity and inhibited the growth of all MRSA strains at 3.13 to 6.25 Âľg/ml [64]. Anti-MRSA activity of Sofora flavonone G(SFG) and synergy between SFG and antibacterial agents against MRSA by means of minimum inhibitory concentration were demonstrated. The minimum inhibitory concentrations (MICs) of SFG against 27 strains of MRSA was found in the range of 3.13 to 6.25 Âľg/ml [65]. Several authors have demonstrated time kill kinetics of various plant extracts and essential oils against drug resistant bacteria. Tea tree oil showed a rapid decrease in the survival of different pathogenic drug resistant bacteria including Enterococcus faecalis, methicillin resistant S. aureus, and Pseudomonas aeruginosa in the first two hr of incubation. The oil killed the MSSA strains within the 30 min while two MRSA strains were killed in 1.5 hr