In Vitro Studu of Antibacterial Activity of Oregano (Origanum Vulgare)

Background and Purpose: Screening of natural medicinal plants is common because many infectious diseases are known to have been treated with herbal remedies throughout the history of mankind. Even today, plant materials continue to play a major role in primary health care as therapeutic remedies in many developing countries. In search for alternative ways of infectious disease control; essential oil and aqueous decoction from oregano were used in the present study to check their antibacterial properties against Gram-negative and Gram-positive using standard disc diffusion method In vitro. Experimental approach: Antimicrobial assay was performed by the well diffusion method using soft 0.8% agar. Agar medium was added to sterile Petri dishes seeded with 100 μl of each test bacterial strains. Wells of equal distance were dug on the seeded plates. Each well was filled up with 100 μl of the solutions tested. After adjusting the pH at 6.5 by NaOH, the activity of the plant extracts was checked. The plates were incubated at 37°C for 48 hours. The antibacterial activity was assayed by measuring the diameter of the inhibition zone formed around the well. Minimum bacteriocidal concentration (MBC):The MBC were carried out to check whether the test microbes were killed or only their growth was inhibited. Nutrient Agar agar was prepared and sterilized at 121 o C for 15 minuts, the medium was poured into sterile petridishes and were allowed to cool and solidify. The contents of the MIC in the serial dilution were then subcultured onto the prepared medium, incubation was made at 37 o C for 24 h, after which each plate was observed for colony growth. The lowest concentration of the extracts without a colony growth was recorded as the MBC; Minimum inhibitory concentrations(MICs): The estimation of MIC of the crude extracts was carried out using the broth dilution method [11] and MICs were read in mg/ml after over night incubation at 37 o C. All experiments were made in replicate. Key Results: This study has demonstrated that solution of oregano at concentration 50 mg/ml for 24 hours notably inhibited growth of S. aureus (29.10 mm mean zone of inhibition), Е. aerogenes (26.20 mm mean zone of inhibition) and E. coli (24.03 mm mean zone of inhibition). On the contrary, solutions of oregano at concentration 50 mg/ml had no activity against L. monocytogen (20.40 mm mean zone of inhibition) and S. Typhymurium(20.37 mm mean zone of inhibition). MIC of solutions of oregano at concentration 50 mg/ml for 24 hours notably inhibited growth of S. aureus 745, L. monocytogen 863 and S. Typhynurium 745. MIC of solutions of oregano at concentration 6.25 mg/ml for 24 hours notably inhibited growth only of E. coli 3398. In contrast, MIC of solutions of oregano at concentration 3.125 mg/ml for 24 hours notably inhibited growth of Е. aerogenes 3691 and B. subtilis 6633. The probable reason for the higher MIC reported for some bacteria is the complex structure of their cell wall. MBC of solutions of oregano at concentration 50 mg/ml for 24 hours notably inhibited growth only of Gram-positive bacteria L. monocytogen 863. For Gram-positive bacteria S. aureus 745, MBC is 25 mg/ml. For Е. aerogenes 3691, E. coli 3398 and B. subtilis 6633 MBC is 3.125 mg/ml. Conclusions and Implications: Based on the results obtained we can conclude that the examined solutions of oregano has bactericidal activity towards both Gram-positive bacteria and Gram-negative bacteria, but in different concentrations. The results obtained show the existence of antibacterial activity of solutions of oregano towards various pathogenic bacteria. The study demonstrated that oregano represents an economic source of natural mixtures of antibacterial compounds that can be as effective as modern medicine to combat pathogenic microorganisms and safe alternative to treat infectious diseases. The solutions of oregano at 50 mg/ml, 25 mg/ml, 12.5 mg/ml, 6.25 mg/ml and 3.125 mg/ml concentrations showed significantanti bacterial activity on selected pathogens inclinical isolates.