The treatment of microbial infections requires a large use of antibiotics which is, partially, responsible for the appearance of resistant strains to antibiotics in dairy cows. However, many photochemical compounds, including the essential oils, are becoming interesting as potential source of natural bioactive molecules. The antibacterial activity of the studied essential oils was evaluated by aromatogram and microdilution in medium liquid. The results show that the essential oil of Thymus fontanesii has the biggest antibacterial action against all the bacterial strains comparing with the Eucalyptus oil. However, the aqueous extracts of Thymus fontanesii and Eucalyptus indicate a moderate antibacterial activity against the strains of Staphylococcus aureus. On the other hand there is no effect on Escherichia coli strains. The most strong activity inhibitory was get with the essential oil of Eucalyptus against Staphylococcus aureus strains with CMI of 0.39 μl/ml for Staphylococcus aureus ATCC and 1.562 μl/ml for Staphylococcus aureus pathogen in comparison with the essential oil of Thymus fontanesii which is more active against the Escherichia coli strains. The aqueous extract of Eucalyptus showed the best CMI and CMB against the Staphylococcus aureus strains in comparison with the aqueous extract of Thymus fontanesii. Comparative tests to the activity have been made with cefoxitin and gentamicin discs.

Abstract
INTRODUCTION
MATERIALS AND METHODS
    Essential oil and the aqueous extracts used in the experiment
    Evaluation of the antibacterial activity
RESULTS
    The antibacterial activity
    Evaluation of the antibacterial activity of oils and crudeextracts of plants Thymus fontanesii and Eucalyptus
DISCUSSION
CONCLUSION
REFERENCES

• ADIDA Houria(Antibiotics, Antifungal: Physical Chemistry, Synthesis and Biological Activity, Laboratory, Department of Biology, Faculty of Natural Sciences and Life Sciences and Earth and the Universe) Corresponding Author.
• SELLES Sidi Mohammed Ammar(Laboratory of Research on Local Animal Products, Ibn-Khaldoun University of Tiaret/Institute of Veterinary Science, Ibn-Khaldoun University of Tiaret)
• BEY BOUMEZRAG Amina(Antibiotics, Antifungal: Physical Chemistry, Synthesis and Biological Activity, Laboratory, Department of Biology, Faculty of Natural Sciences and Life Sciences and Earth and the Universe)
• DRAOUI Hanane(Antibiotics, Antifungal: Physical Chemistry, Synthesis and Biological Activity, Laboratory, Department of Biology, Faculty of Natural Sciences and Life Sciences and Earth and the Universe)