Screening for in vitro antimicrobial activity of ocimum graveolens crude extract

Abstract

Background Despite the availability of effective chemotherapeutic agents the fight against diseases is very far from due to emergences of drug resistance against several conventional chemotherapeutic agents .Resistance of microbes to antimicrobial agents usually oblige the health care providers to shift to more efficacious but expensive drugs which are not affordable by majority in developing countries. Plants are rich in a wide variety of secondary metabolites, such as tannins, terpenoids, alkaloids, and flavonoids, which have been found in vitro to have antimicrobial properties. Ethno pharmacologists, botanists, microbiologists, and natural-products chemists are combing the Earth for phytochemical and "leads" which could be developed for treatment of infectious diseases.

Objective The study was conducted in order to screen for in vitro antimicrobial activity of crude plant extract of Ocimum graveolens specifically the antifungal and antibacterial activities.

Methods The in vitro antimicrobial activity of crude plants extract Ocimum graveolens which were collected from lake zone region was tested on strains of standard reference microorganism namely Candida albicans, Pseudomonas aurignosa, Escherichia coli , and staphylococcus aureus. The antimicrobial activity of the crude plant extracts of varying concentrations 5, 10 20 and 75mg/ml by dissolving in (Dimethylsulphoxide) and evaluated by microdilution method with modified MTT methods microtitre plate with 96 wells was used. Sterile Sterile Mueller broth and Sabouraud broth was used as a culture media for bacteria and fungi respectively. About 120ul of culture media, various concentration of extract ranging from 1 to 128 pl were serially added into given wells, finally a 5-pl of microbial sunspension with previously adjusted turbidity to match that of McFarland O.5were also added in each wells .The plate was aerobically overnight incubated at 37Dc then 5pl of MTT was added to each well and incubated for another 4 hours before an addition of 20 ul of detergent (sodium dodecyl sulfate) was added to the wells and incubated for 1 hour. After that absorbance reading of each well was taken by using spectrophotometer machine.

RESULTS Concentration -dependent phenomenon was observed for the non flowering O. graveolens crude extract that is an increase in concentration was direct proportional to the increase in absorbance. This was demonstrated by a positive correlation between absorbance and Concentration (R: 0.875, P=0.001).Candida albicans, was apparently the most resistant microorganism at higher concentration and Pseudomonas demonstrated to be at least the most susceptible.

A negative correlation between absorbance and concentration was observed (Pearson R0.356, P= 0.001), for the flowering O.grave0fens crude extract, the flowering O.graveolens crude extract, that is an increase of concentrations led to decrease in absorbance. Of the four tested microorganisms Stphylococus aureus was the most resistant to the crude extract while Escherichia coli was the most susceptible. However, T-test revealed no the statistical significance difference between the two test microorganisms with respect to the absorbance.

Conclusion The flowering Ocimum graveolens crude plant extract exhibited relatively stronger antimicrobial activity on the test microorganisms compared to the non-flowering extract. Pseudomonas isolates were the most resistant of the four test microorganism against the flowering crude extract while E. coli was the most susceptible. The extract has also shown activity on Candida albicans O. graveolens non flowering crude extract, seemed to support microbial growth, which leads to increase of absorbance as the extract’s concentrations increase, contrary to the flowering crude extract.