**1. Introduction**

344 Antimicrobial Agents

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Antibacterial agents of plant origin have vast therapeutic potential. They are valuable in the treatment of infectious diseases while simultaneously extenuating many of the side effects that are often associated with synthetic antibacterial agents. The beneficial medicinal effects of plant materials typically result from the combinations of secondary metabolites such as alkaloids, steroids, tannins, phenol compounds, flavonoids and resins fatty acids gums which are capable of producing definite physiological action on body (Paul *et al*., 2006). Nowadays, multiple drug resistance has developed due to indiscriminate use of commercial antimicrobial drugs commonly used in the treatment of infectious disease. In addition to this problem, antibiotics are sometimes associated with adverse side effects on the host including hypersensitivity, immune-suppression and allergic reactions. This situation forced scientists to search for new antimicrobial substances. Giving the alarming incidence of antibiotic resistance in bacteria of medical importance, there is a constant need for new and effective therapeutic agents. Therefore, there is a need to develop alternative antimicrobial drugs for the treatment of infectious diseases from medicinal plants. Biodiversity is a precious source for modern biotechnology. It is a source which potentially holds innovative and sustainable solutions to a broad range of important problems for modern society. Improved cooperation between the natural product chemists and the microbiologists is a productive step to speed up the process of evaluating these potentialities. Moreover, microbiologists and natural product chemists in tropical countries, with the richest flora and fauna placed right at their door step have a very central position. They are essential for building up international scientific cooperation, with the objective of expanding our understanding of biological and biochemical diversity, and based on this bringing forward more biological solutions. The entire process is built on a principle of fairness and equity in sharing of the benefits and respecting the State's sovereign right to its own resources. After figuring out the chemical structures of secondary metabolites, it is considered crucial to know how useful these molecules might be in terms of medicinal properties. During the past 40 years, numerous novel compounds have been isolated from different plants and marine organisms and many of these have been reported to have core biological activities, some of which are of interest from the point of view of potential drug development (Lene, 1996; Gerald, 2001).

*Andrographis paniculata* (Burm.f) Wall. ex Ness: A Potent Antibacterial Plant 347

25 mg/mL crude powder. Moreover, administration of a single oral dose of powder, up to 6 g, to healthy volunteers in a randomized crossover manner or daily administration of 0.12-24 g/kg body weight to rats for six months also failed to show any *ex vivo* antibacterial activity. A similar conclusion was also reached by Zaidan *et al.* (2005) who found crude aqueous extract of leaves had no activity against *Escherichia coli* or *Klebsiella pneumoniae* but exhibited significant antimicrobial activity against gram positive *S. aureus*, methicillin-resistant *S. aureus* (MRSA), and gram-negative *Pseudomonas aeruginosa*. However, Singha *et al*. (2003) reported significant antibacterial activity of an aqueous extract and attributed it to the combined effect of andrographolides and arabinogalactan proteins. In contrast, Xu *et al*. (2006) investigated the antimicrobial activity using *A. paniculata* methanolic and aqueous extracts and authentic andrographolide against nine human bacterial pathogens. Their results indicated methanolic extracts of *A. paniculata* to be active against only two of the pathogens, while authentic andrographolide did not show any activity. They concluded that the observed antimicrobial activity was due to other active principle(s) present in the extracts that were used in the investigation. The ethanol extract was also reported to be devoid of significant antibacterial activity against enterohemorrhagic strains of *E. coli* (Voravuthikunchai *et al*., 2006). In another study, Sahalan *et al*. (2010) reported the antibacterial activity of methanol extract of the leaves of *A. paniculata* against *Staphylococcus aureus*, *Bacillus subtilis*, *Streptococcus epidemidis*, *Escherichia coli*, *Klebsiella pneumoniae* and *Pseudomonas aeruginosa*. Abubacker and Vasanth (2010) reported the antibacterial value of ethanol leaf extract against pathogenic bacteria *Escherichia coli, Klebsiella peneumoniae, Proteus vulgaris* and *Streptococcus pneumonia.* Bioactive compound andrographolide was isolated from the leaf. The results revealed that the ethanol leaf extract and andrographolide compound are potent in inhibiting these bacteria and this work highlights that the inhibitory effect is on par with standard antibiotics. Kataky and Handique (2010) reported antimicrobial activity of various organic and aqueous extracts of eight-months old micropropagated plantlets of *A. paniculata* against gram negative (*Klebsiella pneumoniae*, *Escherichia coli*, *Pseudomonas aeruginosa*), gram positive (*Staphylococcus aureus* and *Bacillus subtilis*) bacteria. Among all tested extracts, chloroform extract showed strong inhibitory activity with all the microbes tested. Out of the five microbial test organisms *Staphylococcus aureus* was the most susceptible. The minimal inhibitory concentration (MIC) of the chloroform extract ranged from 15.625 μg/mL to 31.5 μg/mL. Roy *et al*. (2010) reported the antibacterial potential of chloroform extract of the aerial parts of *A. paniculata* against *E. faecalis* (35 mm), followed by *E. cloacae* (30 mm) *P. aeruginosa* (28 mm) and *E. coli* (25 mm). Least inhibition zone was observed against *S. aureus* (15 mm). Though the inhibition zone observed against *S. typhimurium* was only 18 mm, it is noteworthy when comparing it with that of the control result. Out of the 9 pathogenic strains tested, 7 strains showed inhibition zones comparable with that of the control (amikacin) used. The chloroform extract antimicrobial activity seen against all the tested gram-negative opportunistic and pathogenic bacteria is very encouraging and important considering the role of gram-negative bacteria in noscomial infections leading to increased morbidity and mortality rates. Sule *et al*. (2011a) reported that *A. paniculata* extracts have bactericidal characteristic against most of the Gram positive bacteria and

bacteriostatic activity against both Gram negative and Gram positive bacteria.

*A. paniculata* has already been reported for its significant antibacterial potential by many researchers across the world (Leelarasamee *et al*., 1990; Singha *et al*., 2003; Zaidan *et al*., 2005;

**4. Objective of current study** 

In this context, *Andrographis paniculata* (Burm.f.) Wall. ex Nees., could be a potential source to develop new efficacious antibacterial drugs. *A. paniculata* (*Acanthaceae*) (King of Bitters) is an annual herbaceous plant and is widely cultivated and traditionally used in Southern Asia, China and some parts of Europe. *A. paniculata* has been effectively used in traditional Asian medicines for centuries. In traditional medicine, *A. paniculata* is widely used to get rid of a body heat, dispel toxins from the body, prevents common cold, upper respiratory tract infections including sinusitis and fever (Gabrielian *et al*., 2002) and as an antidote against snakes and insects poisons (Samy *et al*., 2008)*. A. paniculata* has been reported to exhibit various mode of biological activities *in vivo* as well as *in vitro* viz., antiviral (Wiart *et al*., 2000), anti-inflammatory (Wen *et al*., 2010), antihuman immunodeficiency virus (HIV) (Calabrese *et al*., 2000), immunomodulating/immunostimulatory (Iruretagoyena *et al*., 2005), anticancer activity (Li *et al*., 2007; Geethangili *et al*., 2008) and antibacterial activity (Leelarasamee *et al*., 1990; Singha *et al*., 2003; Zaidan *et al*., 2005; Xu *et al*., 2006; Voravuthikunchai *et al*., 2006; Mishra *et al*., 2009; Sahalan *et al*., 2010; Abubacker and Vasanth, 2010; Kataky and Handique, 2010; Parvataneni and Koduru, 2010; Roy *et al*., 2010; Sule *et al*., 2011a, 2011b).
