**8. Conclusion**

356 Antimicrobial Agents

Antibiotics offer the core basis for the effective therapy of chronic bacterial infections. However, the high genetic variability of bacteria enables them to rapidly elude the action of antibiotics by developing antibiotic resistance. As resistance becomes more common, there becomes a greater need for alternative treatments. However, despite a push for new antibiotic therapies, there has been a continued decline in the number of newly approved drugs (Bächi, 2002). According to the World Health Organization (WHO) report on infectious diseases in 2000, overcoming antibiotic resistance is the major issue of the WHO for the next millennium. Hence, the last decade witnessed an increase in the investigations on plants as a source of human disease management (Paul *et al*., 2006). *A. paniculata* is common throughout Southeast Asia and India and is extensively used by traditional healers for the treatment of a wide variety of ailments (Coon and Ernst, 2004). The antibacterial activity of *A. paniculata* extracts are well known (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). Whilst many studies have isolated and characterized *A. paniculata* compounds, no study has ever determined the antimicrobial activity of isolated compounds so far. In the present experiment, the MeOH extract of the whole plant of *A. paniculata* showed broad spectrum antibacterial activity. 3-*O*-β-D-glycosyl-14-deoxyandrographolide and 14-deoxyandrographolide were isolated as active principles, which may serve as lead for the development of new pharmaceuticals that might address the unmet therapeutic needs to cure chronic bacterial infections effectively. The obvious fields where the natural product chemist can harvest benefits from a cooperation with the microbiologists are development of bioassay for efficient monitoring of isolation and purification of new compounds; bioassay fingerprinting to help early de-selection of known compounds (hereby supplementing the chemical data and giving additional avenues for tapping into the computerized data bases); activity spectrum to help de-selecting the very toxic compounds; obtaining a sharper focus in the natural product chemistry work on biologically active compounds. Novel and potentially useful may be of more interest than to go exclusively for just novelty (Lene, 1996). Bio-autography provides more information about plant compounds requires a smaller weight of sample and can be used for the bioassay-guided isolation of biological active compounds, simplifying the process of the

identification and isolation of the active compounds (Rahalison *et al*., 2007).

The antibacterial activity measured by the cup-plate agar diffusion method was more prominent on the Gram-positive bacteria (*S. aureus, M. luteus* and *S. pyogenes*) than the Gram-negative bacteria (*P. mirabilis* and *P. aeruginosa*). Gram-positive bacteria were the most susceptible to growth inhibition by MeOH extract of *A. paniculata* whole plant. The greater susceptibility of Gram-positive bacteria has been previously reported for South American (Paz *et al*., 1995), African (Kudi *et al*., 1999) and Australian (Palombo and Semple, 2001) plant extracts. Susceptibility differences between Gram-positive and Gram-negative bacteria may be due to cell wall structural differences between these classes of bacteria. Gram-negative bacteria have an outer phospholipid membrane carrying the structural lipopolysaccharide components. This makes the cell wall impermeable to antimicrobial chemical substances. The Gram-positive bacteria tested were more susceptible to the plant extracts because it is well known that all Gram-positive bacteria have an outer peptidoglycan layer which is not

**7. Discussion** 

The thin layer chromatography bioautography-guided strategy was successfully used to isolate two antibacterial compounds from MeOH extract of *A. paniculata* whole plant for the first time. The 3-*O*-β-D-glycosyl-14-deoxyandrographolide and 14-deoxyandrographolide demonstrated signicant antibacterial activities against the selected microbial strains. Quantitative HPLC and TLC analysis conrmed that these isolated compounds are predominate components in whole plant MeOH extract, indicating their signicant contribution to the overall antibacterial activity. Further investigation of the activities of these compounds and their potential use in the treatment of bacterial diseases are still sought.
