Mirabilis jalapa was collected in Nagerkovil Dist of Tamilnadu. The voucher specimen has been deposited at the museum of the Dept. of Pharmacognosy , K. M. College of Pharmacy, Madurai and authenticated by a taxonomist.

The shade dried and powdered leaves were extracted successively with petroleum ether, benzene, chloroform, ethanol , methanol by soxhlet extractor and water extract by cold maceration.

Preliminary phytochemical investigation ^5,6,7,8

The qualitative chemical test of various extracts of Mirabilis jalapa was carried out using standard procedure showed the presence of glycosides, saponins, tannins .

Micro organisms used

Gram - positive bacteria : Staphylococcus aureus, Staphylococcus epidermidis, Bacillus subtilis

Gram - negative bacteria : Escherichia coli, Pseudomonas aeruginosa, Klebsiella

pneumoniae

Fungi : Candida albicans

Antimicrobial activity testing of disc- diffusion assay^9,10,11

Various extracts were dissolved in the same solvent to a final concentration of 30mg/ml and sterilized .Antimicrobial tests were then carried out by disc-diffusion method. The density of the bacterial suspension was standardized by using Mac Farland standard method. The discs were impregnated with 10µl of the extracts (300/disc) at the concentration of 30mg/ml and placed on the inoculated agar. Negative controls were prepared using the same solvents employed to dissolve the plant extracts. Ciprofloxacin 10µg/disc and Amphotericin B 100 units/disc were used as positive reference standards. The inoculated plates were incubated at 37 ⁰C bacteria and 25 ⁰C for fungi (Monica Cheesbrough, 1985).

Micro dilution assay^12,13

The minimal inhibition concentration values were also studied for the microorganisms in disc-diffusion assay. The inoculums prepared from 12-hour broth cultures and suspensions were adjusted to 0.5 Mc Farland standard turbidity. The Mirabilis jalapa extract dissolved in 10% Dimethyl sulfoxide were first diluted to the highest concentration (500µg/ml) to be tested, and then serial two fold dilutions were made in a concentration range from 7.8-500µg/ml. minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of Mirabilis jalapa extract against bacteria and minimum fungicidal concentration against C.albicans were determined based on a micro-well dilution method .

Disc diffusion assay

The antimicrobial activity of Mirabilis jalapa leaves extracts against microorganisms examined in the present study and their potency were quantitatively assessed by the presence or absence of inhibition zones and zone diameters, minimum inhibitory concentration and minimum bactericidal concentration values. All the extracts at concentration of 300µg/ml inhibited the growth of C.albicans. All extracts had inhibitory activity against gram positive and gram negative bacteria (Table 1) except petroleum ether extract.

Figure 1

Table 1. Antimicrobial activity of leaves of various extracts against the bacterial and fungal strains tested based on Disc-Diffusion method

Minimum inhibitory concentration (Table 2 )

MIC of Mirabilis jalapa was as low as 18µg/ml against E. coli . The concentration was at 27µg/ml for Bacillus subtilis, 33µg/ml Klebsiella pneumoniae , Mirabilis jalapa at concentration of 20µg/ml inhibited the growth of Staphylococcus aureus, Staphylococcus epidermis 21µg/ml, Pseudomonas aeruginosa 27µg/ml and 30µg/ml for C.albicans.

Minimum Bactericidal and Fungicidal Concentration (Table 2)

The bactericidal and fungicidal maximum concentration of Mirabilis jalapa is 37µg/ml for Staphylococcus aureus, 39µg/ml Staphylococcus epidermis, Pseudomonas aeruginosa 36µg/ml, 36 µg/ml for C.albicans , 33µg/ml for Bacillus subtilis , Klebsiella pneumoniae 36µg/ml and for E.coli 35µg/ml.

Figure 2

Table 2. The MBC and MIC values of leaves of various extracts against the bacterial and fungal strains tested in Microdilution Assay