2 nd International CIGR Workshop on Food Safety: Technologies and Innovations Applied to Food Safety 5 th - 6 th July 2012, Valencia, Spain 117 ANTIBIOTIC SENSIBILITY OF LISTERIA INNOCUA IN THE PRESENCE OF NATURAL ANTIMICROBIAL AGENTS S. F. Zanini 1,* , A. Rosenthal 2 , A. B. Silva-Angulo 3 , M. Sanz-Puig 1 , D. Rodrigo 4 , A. Martínez 4 1 CNPq Postdoctoral Fellowship. Espirito Santo Federal University, Department of Veterinary Medicine, Alegre, Brazil. 2 Embrapa Food Technology, Av. das Américas 23020-470, Rio de Janeiro, RJ, Brazil. 3 Departamento de Biotecnologia Agroalimentaria, Biopolis S.L., Avda. Agustín Escardino, 9, 46980 Paterna, Spain. 4 Department of Preservation and Food Quality, Instituto de Agroquímica y Tecnología de Alimentos (IATA-CSIC), Avda. Agustín Escardino, 7, 46980 Paterna, Spain. *Corresponding author. Tel.: +55 283 552 8653. E-mail: smzanini@gmail.com Abstract. Brazilian agribusiness became increasingly competitive on the global agribusiness stage primarily in the animal production. In the first quarter of 2011 were slaughtered 8.160 million of pigs and 1.306 billion of chickens. To ensure the productivity and competitiveness of the sector, the use of drugs as growth promoters is a common practice. However, the use of substances as antimicrobial growth promoters has been discussed and is subject to a series of rules because the literature has been reporting the presence of bacteria resistant. The concern about the growth of bacterial resistance to antibiotics has stimulated the search for alternatives that will replace these substances as growth promoters. The aim of this study was to evaluate the antibiotic sensibility of Listeria innocua (CECT 910) and Listeria monocytogenes (CECT 4032) in the presence of natural antimicrobial agents. The DMSO was used as dilution agent for obtaining the levels of 0.100 and 0.175 μL/mL for carvacrol and levels of 0.150 and 0.250 μL/mL for citral. Assessing the strains of L. monocytogenes and L. innocua, it was verified that the sensibility to erythromycin was of the 0.250 μg/mL. There was reduction of the minimal inibitory concentration (MIC) of erythromycin in the presence of antimicrobials carvacrol or citral in cultures of L. innocua and L. monocytogenes to 0.094-0.125 μg/mL. In this study the MIC of bacitracin in cultures of L. innocua and L. monocytogenes was of 32 μg/mL. However, there was reduction of MIC in the presence of antimicrobials carvacrol or citral. The MIC of colistin in cultures of L. innocua and L. monocytogenes was reduced in the presence of antimicrobial carvacrol or of citral from 96-128 μg/mL to 4 μg/mL. The results obtained in this study showed that the combined use of antibiotics with natural antimicrobial resulted in a synergistic effect demonstrated by the reduction of the MIC in cultured of L. monocytogenes and L. innocua. Keywords . Minimal inibitory concentration, antibiotics, citral, carvacrol, Listeria. Introduction Brazilian agribusiness became increasingly competitive on the global agribusiness stage primarily in the animal production. In the first quarter of 2011 were slaughtered