Phytochemical Screening, Cytotoxicity and Antibacterial Activities of Two Bangladeshi Medicinal Plants

INTRODUCTION

Aglaonema Schott is included in the family of Araceae. This medicinal plant is widely distributed in tropical Asia. Malay, Archipelago and Papuasia (Mayo et al., 1997). The genus Aglaonema was revised by Nicolsonm (1969) who recognized 21 species and 2 sections. The genus Aglaonema is known as Aglaonema hookerianum Schott in Bangladesh (Ara et al., 2005). The plant is available in Chittagong Hill Tracts and Sylhet. The root infusion of Aglaonema hookerianum Schott taken orally is used for the treatment of conjunctivitis and constipation (Rahman et al., 2007). On the other hand, the local name of Lannea grandis Engl is Jikkha belonging to the family of Anacardiaceae. The leaves of Lannea grandis Engl were used as diuretic in case of urinary problems. This medicinal plant is also utilized by the Garo Tribal Healers of Netrokona District in Bangladesh (Rahmatullah et al., 2009). The meristem of Lannea grandis was used to treat dog bites, while the gum of the same plant was mixed with seeds of Astercantha longifolia to treat low sperm count (Rahmatullah et al., 2010). Due to lack of scientific data, the present study was conducted to investigate the cytotoxic and antimicrobial activities of the leaves of Aglaonema hookerianum Schott and Lannea grandis Engl.

MATERIALS AND METHODS

Plant materials and preparation of the extract: The medicinal plants Aglaonema hookerianum Schott and Lannea grandis Engl selected for this study were collected from Sylhet and Netrokona, respectively during the months of September-October (2009) at day time. The leaves of Aglaonema hookerianum Schott and Lannea grandis Engl. were dried at room temperature under shade and were ground into a coarse powder with the help of a suitable grinder. About 200 g of powdered material of each medicinal plant was taken in clean, flat bottomed glass container and soaked in 1000 mL of 99.8% ethanol. The containers with its contents were sealed and kept for a period of 14 days accompanied by continuous shaking with a shaker. The solvent extracted materials were filtered and the resulting filtrates were concentrated under reduced pressure. Finally, the extracts of both plants were preserved until required.

Culture media and test microorganisms: The media used for bacteria was Nutrient agar and the test organisms used in this study included both gram-positive bacteria such as (Bacillus subtilis, Bacillus megaterium, Staphylococcus aureus) and gram negative bacteria such as Pseudomonas aeruginosa, Escherichia coli, Shigella dysenteriae, Salmonella typhi, Salmonella paratyphi and Vibrio cholerae).

Standard drug: Amoxycillin was used as a standard drug in this research work and the drug was collected from Square Pharmaceuticals Limited, Dhaka, Bangladesh.

Preliminary phytochemical screening: The ethanolic extracts of the leaves of Aglaonema hookerianum Schott and Lannea grandis Engl. were subjected to preliminary phytochemical screening as per procedure to identify the presence of various phytochemicals. Phytochemical screening of the extracts were performed using the following reagents: Alkaloids with Dragendroff’s reagent and Mayer’s reagent, Steroids with sulphuric acid, Glycosides with sodium hydroxide, Tannins with ferric chloride and potassium dichromate solutions, Reducing sugars with Fehling’s solution (A and B) and Benedict’s solution, Saponins with the ability to produce foams. Gum was also tested using Molish reagent and concentrated sulphuric acid (Trease and Evans, 1989).

Cytotoxic activity: The cytotoxic activity of the crude ethanolic extracts of leaves of Aglaonema hookerianum Schott and Lannea grandis Engl was tested on brine shrimp nauplii according to brine shrimp lethality bioassay (Meyer et al., 1982). From this study, the lethal concentrations LC₅₀(μg mL^-1) and LC₉₀ (μg mL^-1) of the ethanolic extracts were determined.

In-vitro antimicrobial assay: The extracts obtained from the leaves of Aglaonema hookerianum Schott. and Lannea grandis Engl. were studied for antimicrobial activity using the agar disc diffusion method (Bauer et al., 1966). The concentrations of ethanolic extracts of the plants and the standard drug, Amoxicillin used in this study were 500 and 10 μg disc^-1, respectively.

RESULTS AND DISCUSSION

Phytochemical screening: The results of phytochemical screening of the ethanolic extracts of Aglaonema hookerianum Schott and Lannea grandis Engl were summarized in Table 1. Phytochemical study of ethanolic extracts of Aglaonema hookerianum Schott revealed the presence of alkaloid, glycoside, tannin, reducing sugar, saponin and gum. Alkaloid, steroid, tannin, reducing sugar, saponin and gum were also identified in the ethanolic extract of Lannea grandis Engl.

In-vitro antimicrobial activities: The ethanolic extracts of leaves of Aglaonema hookerianum Schott and Lannea grandis Engl were used in the present study to investigate their antimicrobial potentials where both gram-negative and gram-positive bacteria were used. The results of antimicrobial activities of extracts were shown in Table 2 and 3. The ethanolic extracts of leaves of Aglaonema hookerianum Schott showed significant antimicrobial activity (zone of inhibition: 15.08±0.45 mm to 20.37±0.45 mm) against all tested bacterial strains and the highest zone of inhibition was observed against S. paratyphi (20.37±0.45 mm). The ethanolic extracts of Lannea grandis Engl leaves also showed significant activity against all tested bacteria with zone of inhibition ranging from 13.93±0.09 mm to 18.25±0.54 mm.

Cytotoxic activities: The results obtained from the brine shrimp lethality bioassay showed that the ethanolic extract of both plants possessed cytotoxic activities and the values of LC₅₀(μg mL^-1) of Aglaonema hookerianum Schott and Lannea grandis Engl were 5.25 (μg mL^-1) and 5.75 (μg mL^-1), respectively whereas LC₉₀ (μg mL^-1) values of Aglaonema hookerianum Schott. and Lannea grandis Engl. were 10.47 (μg mL^-1) and 9.55 (μg mL^-1), respectively (Table 4 and 5). The values of LC₅₀ (μg mL^-1) and LC₉₀ (μg mL^-1) were deduced from the best-fit line slope.

Table 1:	Results of preliminary screening of ethanolic extracts of leaves of the medicinal plants

Table 2:	Antimicrobial activities of ethanolic extract of Aglaonema hookerianum Schott. and standard drug, Amoxicillin

Table 3:	Antimicrobial activities of ethanolic extract of Lannea grandis Engl. and standard drug, Amoxicillin

Table 4:	Brine shrimp lethality bioassay of ethanolic extract of Aglaonema hookerianum Schott. leaves

Table 5:	Brine shrimp lethality bioassay of ethanolic extract of Lannea grandis Engl. leaves

DISCUSSION

Very few research works were done on the cytotoxicity and antibacterial activities of the ethanolic extracts of the plants. The phytochemical screening showed the presence of alkaloid, glycoside, tannin, reducing sugar, saponin and gum in the ethanolic extracts of Aglaonema hookerianum Schott. Alkaloid, steroid, tannin, reducing sugar, saponin and gum were also identified in the ethanolic extract of Lannea grandis Engl. The present study revealed significant antibacterial activities of the medicinal plants against all of tested bacterial strains. The results of antimicrobial activities showed that S. paratyphi and S. dysenteriae were the most sensitive bacterial strains to the ethanolic extracts of Aglaonema hookerianum Schott and Lannea grandis Engl with significant zone of inhibition (20.37±0.45 and 18.25±0.54), respectively. In addition to this, the study also confirmed the cytotoxic activities of the ethanolic extracts of Aglaonema hookerianum Schott and Lannea grandis Engl showing LC₅₀ values 5.25 and 5.75 μg mL^-1 and LC₉₀, 10.47 and 9.55 μg mL^-1, respectively. Finally, it was concluded that both of the plants possessed cytotoxic and antibacterial activities.

CONCLUSION

In conclusion, the results of this study have shown that both plants are potentially good sources of antimicrobial agents and support the traditional medicinal application of the tested plants. The broad spectra of activity of both plants extracts are promising and the isolation of active constituents of each extract can be the subject of the future researchers.

ACKNOWLEDGMENT

All of the authors would like to thank the authority of International Centre for Diarrhoeal Disease and Research, Bangladesh for giving the bacterial strains. We are also grateful to the Factory Manager of Square Pharmaceuticals Limited for providing the standard drug, Amoxicillin.