Int.J.Curr.Microbiol.App.Sci (2017) 6(3): 1-12 1 Original Research Article https://doi.org/10.20546/ijcmas.2017.603.001 Antimicrobial Activity in vitro of Aqueous Extracts of Oregano (Origanum vulgare L.) and Thyme (Thymus vulgaris L.) Ralitsa Bankova and Teodora P. Popova* University of Forestry, Faculty of Veterinary Medicine, 10 Kl. Ohridski Blvd., Sofia 1756, Bulgaria *Corresponding author ABSTRACT Introduction The wide use of different antibiotic agents for therapy and prophylaxis of bacterial diseases in animals led to selection of resistant microorganisms. Because of this problem Committee for Veterinary Medicinal Products of the European Union stopped the use of some antibiotics and banned their use as growth promoters from 01.01.2006 by Regulation 1831/2003 (Federation, 2003). This decision was justified by the emergence of multy resistant bacterial strains and danger antibiotics become ineffective in therapeutic use in animals and humans. Therefore increasingly emerging trend of looking for new means for use in veterinary medicine, to which it is difficult to build resistance, including biologically active substances of plant origin (Yordanov et al., 2002). Plant extracts are becoming increasingly popular as feed additives for animals replacing antibiotics. They act as antibacterial, antioxidant, anti-cancer means, antifungals, analgesics, insecticides, such as anticoccidial agents and as growth promoters (Levic et al., 2011). There are also a number of studies on antibacterial effect of herbal spices and their essential oils against different types of microorganisms, including food pathogens. International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 6 Number 3 (2017) pp. 1-12 Journal homepage: http://www.ijcmas.com The antimicrobial effect of hot and cold water extracts and infusions of herbs oregano (Origanum vulgare L.) and thyme (Thymus vulgaris L.), prepared in concentrations of 20%, was investigated using the classical agar-gel diffusion method. Pure cultures of 20 pathogenic strains were tested (by 4 strains of Pseudomonas aeruginosa, Klebsiella pneumoniae, Pasteurella multocida, Enterococcus faecalis and Candida albicans). The highest antibacterial and antimycotic effect in vitro exhibited the infusions of both herbs, similar to that of the control broad-spectrum antibiotic thiamphenicol. The inhibitory effect of the infusion of thyme was slightly higher than that of the infusion of oregano. Highest sensitivity to both infusions showed the tested strains of P. aeruginosa and C. albicans, and the lowest - these of P. multocida. The cold water extracts of both studied herbs showed less pronounced antimicrobial effect, which was slightly higher in thyme. The cold extract of oregano showed pronounced antibacterial effect against the strains of P. aeruginosa and K. pneumoniae, but not to those of P. multocida. The hot aqueous extracts of the two herbs manifested weakest antimicrobial activity in vitro. The inhibitory effect of hot water extract of oregano was slightly higher than that of thyme. Keywords Origanum vulgare, Thymus vulgaris, Water extracts, Antimicrobial activity. Accepted: 08 February 2017 Available Online: 10 March 2017 Article Info