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Research Article
Comparative Studies on the Antimicrobial Activity of Leaf Extract from Ocimum basilicum and Antagonistic Activity of Isolates from Refuse on ome Selected Pathogens

Oladunmoye M. Kolawole

International Journal of Biological Chemistry, 2007, 1(1), 69-74.


Refuse samples were screened for the presence of resident bacteria and fungi antagonistic to the growth of some pathogens. Nine bacteria and four fungi were isolated. The pathogens used are clinical isolates which include; Bacillus cereus, Escherichia coli, Klebsiella pneumoniae, Salmonella typhi and Staphylococcus aureus. The assay was carried out using the agar well diffusion method and the plugging method for the bacteria and fungi isolates respectively. Seven bacteria were antagonistic to at least a pathogen and all the fungi isolates showed antagonistic activity against the five pathogens at varying degrees. A 60% ethanol extract from the leaf of Ocimum basilicum (Labiatae) was investigated for in vitro antimicrobial activities against the same set of pathogens. The results showed no antimicrobial activity at concentration of 50, 100 and 200 mg mL-1 while at 300 mg mL-1 there were activities against all the pathogens except Staphylococcus aureus. Bacillus cereus and Salmonella typhi were found to be the most susceptible to the extract. Compared to the plant extracts, none of the bacteria isolated from the refuse showed antagonistic activity against Klebsiella pneumoniae. Actinomyces isolate was the most active of the bacteria isolates and the activity is comparable to that of the leaf extract of Ocimum basilicum. Penicillium isolates has the strongest activity of the fungi isolates and it has a broader zone of inhibition and spectrum of activity than the leaf extract.

ASCI-ID: 34-9

Table 1 and 2). This suggests that the refuse site is populated by myriad if microorganisms’ that were responsible for the biodegradation.

The result of the antagonistic activity of the bacterial isolates (Table 3) indicated that out of the nine organisms, seven were active against the test organisms. Pseudomonas specie and Clostridium specie did not show any antimicrobial activity against any of the test organisms. It might be that the type and the concentration of the metabolite(s) produced could not be enough to inhibit the growth of the test organisms. Actinomyces isolate was the most active with activity against all the test organisms except Klebsiella pneumoniae, with the largest zone of inhibition against Escherichia coli and the least against Salmonella typhi. This study is in conformity with Krasil (1997) who stated that there are very large quantities of actinomycete-antagonists with clearly expressed antimicrobial properties. The resistance of Klebsiella pneumoniae may be due to the presence of a resistance plasmid that codes for resistant gene in the cell. Shigella isolate was the next with a wide spectrum of activity; it showed activity against three of the five test organisms. The reason for the difference in sensitivity between gram-positive and gram-negative bacteria might be ascribed to the difference in morphological constitutions with respect to variation in the complexity of the cell wall and membrane (Mariam et al., 2005).

Listeria, Proteus and Enterobacter isolates inhibited the same set of two test organisms at varying degree, Escherichia coli and Staphylococcus aureus. Acinetobacter and Bacillus species inhibited a test organism each. None of the nine bacteria isolates showed activity against Klebsiella pneumoniae.

The antimicrobial activity of fungi is presented in Table 4. Fungi were found to be more potent in inhibiting the growth of the test organisms than the bacterial. Penicillum isolate was able to show activity against Klebsiella pneumoniae, in contrast to the result obtained with the bacteria isolates. Metabolites from fungi had been shown to have broad spectrum antimicrobial activity (Krasil, 1997). Antagonism by these bacteria and fungi isolates may be due to various specific and non specific metabolic products formed by the isolates. These non-specific substances include organic acids, alcohols, peroxides and other compounds. The specific substances are the antibiotics and bacteriocins. Similar findings have been reported by Krasil (1997). The results obtained with the fungi isolates compared favourably with those of the commercial antibiotics like ofloxacin, chloramphenicol, cefuroxine, ampicillin, gentamycin and tetracycline (Table 6).

The results of the antimicrobial bioassay of the leaf extract of this plant are shown in Table 5. Similar findings have been reported (Adigozel et al., 2005; Calzada et al., 2005). The extract was not active at low concentrations of 50, 100 and 200 mg mL-1. The minimum inhibitory concentration was fond to be at 300 mg m L-1 and the highest antimicrobial activity was observed against Bacillus cereus and Salmonella typhi with both having zones of inhibition of 6.5 mm.

Table 1: Morphological and biochemical characteristics of bacterial isolates from refuse
Glu = Glucose, Dex = Dextrose, Gal = Galactose, Lac = Lactose, Ara-Arabinose, AP = Acid production, GP = Gas production

Table 2: Morphological characterization of fungi

Table 3: Antagonistic activity of bacterial isolates from refuse against test organisms
NI = No inhibition

Table 4: Antagonistic activity of fungi isolates from refuse against test organisms

Table 5: Minimum Inhibitory Concentration (MIC) of leaf extract of ocimum basilicum against test organisms
NI = No inhibition

Table 6: Antimicrobial activity of antibiotics against test organisms (positive control)
NI = No inhibition; OF = Ofloxacin; C = Chloramphenicol; E = Erythromycin, CIP = Ciprofloxacin; CD = Clindamycin; CF = Cefuroxine; AM = Ampicilin, GN = Gentamycin; N = Nitrofurantion; CX = Cephaplexin; CO = Cotrimoxazole; TE = Tetracycline; NB = Norfloxacin; AX = Amoxycillin; AP = Ampicillin/Cloxacillin; FX = Floxapen; AU = Augumentin

Table 7: Qualitative analysis of the phytochemicals in the leaf extract of Ocimum basilium
+ve: Presence of constituent, -ve: Absence of constituent

The antimicrobial action could have been due to inhibition of protein synthesis or other means apart from the inhibition of cell wall synthesis. The antimicrobial activity of the leaf extract against Escherichia coli at a concentration of 300 mg m L-1 was found to be almost comparable to chloramphenicol, gentamycin, nitrofurantion and tetracycline.

The phytochemical screening of the leaf extract of Ocimum basilicum (Table 7) showed that the leaves were rich in anthraquinones, cardiac glycosides, flavonoids, saponins and tannins. These bioactive molecules were known to show medicinal activity as well as exhibiting physiological and antimicrobial activities (Vlictinck and Pieters, 2005).

Comparative evaluation of the antimicrobial activity of the leaf extract and the isolates (Table 3-5), revealed that the leaf extract had a broader spectrum of activity than most of the bacteria isolates. The fungi isolates are more active than the leaf extracts. These observations may be attributed to the nature of the biological active components present in the plant (anthraquinones, flavonoids, saponins, tannins and terpenoids). It has been documented that tannins, saponins and alkaloids are plant metabolites well known for antimicrobial activity (Akinyemi et al., 2005). Also, antibiotics produced from bacteria are commonly known to be narrow in spectrum of activity while the antibiotics from fungi are broad in spectrum of activity (Krasil, 1997).


The results of this study may suggest that Ocimum basilicum extracts possesses compounds with antimicrobial properties against the pathogenic bacteria, therefore offer a scientific basis for the traditional use of the leaf to cure infectious diseases. Also, it suggests that microbial isolates from refuse dumps can produce metabolites with antimicrobial activities against the some pathogens. It was also evident that the leaf extract of Ocimum basilicum is comparable to the fungi isolate, with regards to their spectrum of activity against the pathogens. The leaf extracts and the fungi isolates have a broader spectrum of activity when compared with the bacteria isolates. Therefore the leaf extract may be a better source for drug development.

In vivo study is necessary and should seek to determine toxicity of the active constituents, their side effects, pharmacokinetics properties and diffusion in different body sites. Also, effort should be geared up towards purification and characterization of the metabolites.

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