Journal of Natural Sciences Research www.iiste.org ISSN 2224-3186 (Paper) ISSN 2225-0921 (Online) Vol.4, No.19, 2014 98 Evaluation of Antimicrobial Activities of Albizia zygia DC Leaf Extracts against Some Clinically Important Pathogens Oluyemi Odeyemi 1 , Anthonia Olufunke Oluduro *1 , Oluwole Moses David 2 1. Department of Microbiology, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria 2. Department of Microbiology, Ekiti State University, Ado-Ekiti, Ekiti State, Nigeria * E-mail of the corresponding author: aoluduro2003@yahoo.co.uk. Abstract In vitro antimicrobial effects of aqueous, ethanolic and methanolic extracts of Albizia zygia dc leaf against some clinically important bacterial and fungal pathogens were reported. Following extraction of air dried A. zygia dc leaf by different solvents (water, ethanol and methanol), the filtrates were concentrated in vacuo using rotary evaporator. The antibacterial and antifungal activities were assayed by agar diffusion method on Muller-Hinton Agar (Himedia Laboratories Pvt. Ltd, Vadhani) and Potato dextrose agar (Oxoid, Ltd, Bashingstoke, Hampshire, England) plates, respectively. Standard methods were used to determine the time-kill assay of methanolic extract, the amount of protein and potassium ion leaked in the test bacteria. All the extracts (aqueous, ethanolic and methanolic) did not possess any antifungal property. The aqueous and ethanolic extracts were not active against the test bacteria. Methanolic extract showed significant antibacterial effect on greater percentage of the test bacteria with diameter of zones of inhibition ranging from 3.0 to 21.12 mm at 30 mg/ml and 5.2 to 25.4 mm at 50 mg/ml of the extract. The minimum inhibitory concentration (MIC) of the methanolic extract ranged between 3.75 and 15.3 mg/ml. The methanolic extract of A. zygia leaf showed a significant bactericidal and bacteriostatic activity against Bacillus subtilis and Klebsiella pneumoniae over the time range (15-120 min) at different MIC concentrations. The time-kill assay of methanolic extract of A. zygia against K. pneumoniae was dose dependent. The amount of protein leaked was higher in B. subtilis than K. pneumoniae at 30 μg/ml (P = 0.05). There was no significant difference in the level of K + leaked at 15 μg/ml (1 X MIC) and 30 μg/ml (2 X MIC) of the extract. The methanolic leaf extract of A. zygia showed a considerable inhibitory effect on greater percentage of the test bacterial pathogens, but did not possess antifungal property. The antibacterial potential could be harnessed in the folklore management of infections caused by the susceptible test bacteria. 1.0 Introduction Bacteria develop resistance to antibiotics in a variety of ways, including methods that may decrease the intracellular concentrations of the antibiotic, deactivate the antibiotic, change the binding sites for the antibiotic, and develop adaptations that bypass the need for the binding site targeted by the antibiotic (Kaye et al., 2000). The increasing rate of resistance to antibiotics with its high cost has foster the search for new antimicrobials. Nature has always provided therapeutic means of treating microbial diseases. Nature has endowed several plants with metabolites which are of medicinal importance (Cowan, 1999). Medicinal plants are widely accepted and relatively cheap when compared to orthodox medicines. Apart from their accessibility, medicinal plants have been reported to be the bedrock of modern medicine. However, the shortcomings of traditional medicine include lack of scientific proof of their efficacies, lack of hygienic preparation (in most cases) and lack precise dosage. In Africa, like other developing nations, people rated the advantages of these pharmaceutics far above their shortcomings. Albizia zygia is a deciduous tree 9-30 m tall with a spreading crown and a graceful architectural form (Petzke, 1997). The bark is grey and smooth. Its leaves pinnate, pinnae in 2-3 pairs and broadening towards the apex, obliquely rhombic or obviate with the distal pair largest, apex obtuse, 29-72 by 16-43 mm (Chudnoff, 1984; Petzke, 1997). Albizia zygia is a cheap substitute to some of the known synthetic drugs (Schultes, 1978; Chudnoff, 1984; Ndjakou et al., 2007). It is useful in the treatment of allergy-caused respiratory disorders (Ndjakou et al., 2007). The in vitro anti -Neisseria gonorrhoeae activity of A. zygia has been reported by Mesfin et al. (2012). Different parts of Albizia zygia (bark, fruit, flowers and leaves) have been reported to be used as medicinal remedies (Ndjakou et al., 2007). The study evaluates the antimicrobial potential of A. zygia and its effects on the bacterial cell components 2.0 Materials and Methods 2.1 Source of Microorganisms Microorganisms used in this study were collected from the stock culture unit of the Department of Microbiology, Obafemi Awolowo University, Ile-Ife, Nigeria. The isolates includes Gram positive bacteria: Bacillus cereus OAU 84, Bacillus subtilis OAU 81, Clostridium sporogenes NCTC 532, Enterococcus faecalis NCTC 775, Micrococcus luteus NCIB 196 and Staphylococcus aureus NCIB 8588, while the Gram negative bacteria