The chemical composition and the antimicrobial activity of essential oil from O. applii e O. vulgare were studied against the bacteria Pseudomonas aeruginosa, Salmonella choterasuis, Rhodococcus equi, Micrococcus luteus, Staphylococcus aureus, Escherichia coli, Bacillus subtilis, S. epidermides, Streptococcus faecium e Enterococcus faecium. The essential oil was analyzed by Gas Chromatography Mass Spectroscopy (GC-MS). Antimicrobial activity was evaluated by bioautography with subsequent MIC (Minimal Inhibitory Concentration) determination. The main constituents of O. vulgare e O. applii essential oil was identified (%): p-cimeno, 4,27 and 9,37, a-terpinoleno, 9,13 and 30,23, linalol, 6,35 and 8,75; terpin-4-ol, 24,96 and 3,56 and carvacrol, 17,96 and 11,23, respectively. The essential oil of both Origanum species presented strong activity against Streptococcus faecium and moderate activity against S. choterasuis, S. aureus and B. subtilis.626771Adam, K., Sivropoulou, A., Kokkini, S., Antifungal activities of Origanum vulgare subsp. hirtum, Mentha spicata, Lavandula angustifolia, and Salvia fruticosa Essential Oils against Human Pathogenic Fungi (1998) Journal of Agricultural and Food Chemesty, 46, pp. 1739-1745Adams, R.P., (1995) Identification of Essential Oil Components by Gas Chromatography/mass Spectrometry, , Carol Stream: Allured Publ. Corp. 469pAhmad, I., BEG Antimicrobial and phytochemical studies on 45 Indian plants against multi-drug resistant human pathogens (2001) Journal of Ethnopharmacol, 74 (2), pp. 113-123Aligiannis, N., Kalpoutzakis, E., Mitaku, S., Composition and antimicrobial activity of the essential oils of two Origanum species (2001) Journal Agricultural Food Chemistry, 49, pp. 4168-4170Ali-Shtayeh, M.S.A., Yaghmour, R.M.R.A., Faidi, Y.R.B., Antimicrobial activity of 20 plants used in folkloric medicine in the Palestinian area (1998) Journal of Ethnopharmacology, 60 (3), pp. 265-271Baba-Moussa, F., Akpagana, K., Bouchet, P., Antifungal activities of seven West African Combretaceae used in traditional medicine (1999) Journal of Ethnopharmacology, 66 (3), pp. 335-338Cecanho, R., Koo, H., Rosalen, P.L.J.A., Efeito do extrato hidroetanólico de Mikania laevigata sobre o crescimento bacteriano e a produção de glucamos por estreptococcus do grupo mutans (1999) Reunião da Federação da Sociedade de Biologia Experimental, 14, 1999, Caxambu, 14, p. 290. , Anais... Caxambu, res. 12095Consentino, S., Tuberoso, C.I.G., Pisano, B., In vitro antimicrobial activity and chemical composition of Sardinian thymus essencial oils (1999) Letters in Applied Microbiology, 29, pp. 130-135Eloff, J.N., A sensitive and quick microplate method to determine the minimal inhibitory concentration of plant extracts for bacteria (1998) Planta Medica, 64 (8), pp. 711-713Galli, A., Franzetti, L., Briguglio, D., Attività antimicrobica in vitro di oli essenziali ed estratti di spezie di uso alimentare (1985) Industrie Alimentari, pp. 463-466Hulin, V., Mathot, A.G., Mafart, P., Les proprietés anti-microbiennes des huiles essentielles et composés d'arômes (1998) Sciences des Aliments, 18, pp. 563-582Gergis, V., Spiliotis, V., Poulos, C., Antimicrobial activity of essential oils from Greek Sideritis species (1987) Pharmazie, 45, p. 70Lentz, D.L., Clark, A.M., Hufford, C.D., Antimicrobial properties of Honduran medicinal plants. Short communication (1998) Journal of Ethnopharmacology, 63, pp. 253-263Mahasneh, A.M.A., Adel, M.A., El-Oqlah, A.A.B., Antimicrobial activity of extracts of herbal plants used in the traditional medicine of Jordan (1999) Journal of Ethnopharmacology, 64 (3), pp. 271-276Martínez, M.J., Betancourt, J., Alonso-González, N., Screening of some Cuban medicinal plants for antimicrobial activity (1996) Journal of Ethnopharmacology, 52 (3), pp. 171-174Panizzi, L., Flamini, G., Cioni, P.L., Composition and antimicrobial properties of essential oils of 4 mediterranean Lamiaceae (1993) Journal of Ethnopharmacology, 30 (3), pp. 167-170Pereira, N.A., Pereira, B.M.R., Do Nascimento, M.C., Pharmacological screening of plants recommended by folk medicine as snake venom antifotes. IV. Protection against jararaca venom by isolated constituints (1994) Planta Medica, 60, pp. 99-100Slusarenko, A.J., Longland, A.C., Whitehead, I.M., Convenient, sensitive and rapid assay for antibacterial activity of phytoalexins (1998) Botanica Helvetica, 90 (2), pp. 203-207Souza, E.C., Bactérias ultraresistentes: Uma guerra quase perdida (1998) Ciência Hoje, 1138 (23), pp. 26-35