Does the Folk Medicinal Plant Indigo/era tinctorica has Effective Activity Against Methicillin Resistant Staphylococcus aureus (MRSA)?

Abstract

he Methicillin Resistant Staphylococcus aureus (MRSA) is an important cause of nosocomial infections worldwide. These organisms have become resistant to most of the anti-Staphylococcal antibiotics. In fact, the rate of ti'& emergence of MRSA has been gradually but systematically increased. Although initial MRSA infections were health care associated; the novel investigations show that new strains of MRSA are circulating in the community in places where people are actively gathered (eg: schools, military bases, among football players). These evidences indicate the dire need of inventing new anti-Staphylococcal antibiotics. lndigofera tinctorica is a remedy that has been used in Ayurvedic medicine and in folk medicine to treat various diseases like worm infections, fever, diarrhea and as well as an antiseptic, in addition to being used as a raw material for indigo dye preparations. Extractions were made from shade-dried leaves and flowers of this plant with the use of the hexane, dichloromefuane, ethyl acetate and methanol. The antimicrobial sensitivity test was carried out using the disc diffusion method against Staphylococcus aureus (ATCC 25923) and five different clinically isolated MRSA strains at an initial concentration of 1000 µg/disc. Cefotaxime and Gentamicin, the antibiotics which have been conventionally employed to treat S. aureus infections were used as the positive controls while dichloromethane (DCM)/ methanol (MeOH)/ dimethyl sulfoxide (DMSO) were used as negative controls. Significantly, all the crude extracts of /. tinctorica displayed a zone of inhibition against S. aureus and MRSA strains. Subsequently, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined using broth microdilution method as described by Eloff and Van Staden, 2007. Interestingly, all four different crude extracts demonstrated MIC in the range of 250-500 µg/mL and MBC in the range of 500-1000 µg/mL against the tested micro-organisms. These observations suggest that the tested extracts possess bactericidal activity rather than bacteriostatic activity. This study depicts the promising antimicrobial effects of /. tinctorica against Staphylococcus aureus including MRSA and indicates the potential utilization of this plant for the development of herbal disinfectants against nosocomial infections. Thus experiments are in progress to enhance the intrinsic antimicrobial activity of these plant extracts through a nanotechnological approach and then to evaluate the efficacy against a range of MRSA isolates.