Research Article Phytochemical Prospection and Modulation of Antibiotic Activity In Vitro by Lippia origanoides H.B.K. in Methicillin Resistant Staphylococcus aureus Humberto Medeiros Barreto, 1 Filipe Cerqueira Fontinele, 1 Aldeídia Pereira de Oliveira, 2 Daniel Dias Rufino Arcanjo, 2 Bernadete Helena Cavalcanti dos Santos, 3 Aislan Pereira Lira de Abreu, 4 Henrique Douglas Melo Coutinho, 5 Romezio Alves Carvalho da Silva, 6 Taciana Oliveira de Sousa, 6 Maria das Graças Freire de Medeiros, 6 Antonia Maria das Graças Lopes Citó, 6 and José Arimateia Dantas Lopes 6 1 Laboratory of Microbiology and Immunology, Campus Am´ ılcar Ferreira Sobral, Universidade Federal do Piau´ ı, BR 343, Km 3,5 Bairro Melad˜ ao, 64800-000 Floriano, PI, Brazil 2 Center for Research on Medicinal Plants, Universidade Federal do Piau´ ı, Bairro Ininga, 64049-550 Teresina, PI, Brazil 3 Laboratory of Clinical Microbiology, Universidade Federal da Paraiba, Cidade Universit´ aria, 58051-900 Jo˜ ao Pessoa, PB, Brazil 4 Laboratory of Microbiology, Faculdade de Ensino Superior de Floriano, Bairro Manguinha, 64800-000 Floriano, PI, Brazil 5 Laboratory of Microbiology and Molecular Biology, Regional University of Cariri, Bairro Pimenta, 63105-100 Crato, CE, Brazil 6 Laboratory of Natural Products, Universidade Federal do Piau´ ı, Bairro Ininga, 64049-550 Teresina, PI, Brazil Correspondence should be addressed to Humberto Medeiros Barreto; hmbdoc@gmail.com Received 8 December 2013; Revised 6 January 2014; Accepted 6 January 2014; Published 10 February 2014 Academic Editor: Aramati B. Reddy Copyright © 2014 Humberto Medeiros Barreto et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. he Lippia origanoides H.B.K. ethanol extract (LOEE) and hexane (LOHEX), dichloromethane (LODCM), and ethyl acetate (LOEA) fractions were tested for their antimicrobial activity alone or in combination with antibiotics against a methicillin resistant Staphylococcus aureus (MRSA) strain. he natural products did not show antimicrobial activity against multidrug resistant strain at the clinically signiicant concentrations tested. However, a modulatory efect in the antibacterial activity of the neomycin and amikacin was veriied when LOEE, LOHEX and LODCM were added to the growth medium at subinhibitory concentrations. A similar modulation was found when the natural products were changed for chlorpromazine, an inhibitor of bacterial elux pumps, suggesting the involvement of resistance mediated by elux system in the MRSA tested. he fractions LOHEX and LODCM showed a modulatory activity bigger than their majority compounds (carvacrol, thymol, and naringenin), indicating that this activity is not due to their majority compounds only, but it is probably due to a synergism between their chemical components. hese results indicate that L. origanoides H.B.K. can be a source of phytochemicals able to modify the phenotype of resistance to aminoglycosides in MRSA. 1. Introduction Methicillin resistant S. aureus (MRSA) remains as an impor- tant cause of infectious diseases acquired in hospitals and communities worldwide [1–3]. his pathogen is a common cause of cutaneous and sot tissue infections, as well as inva- sive illness, such as bacteremia, septic arthritis, osteomyelitis and necrotizing pneumonia [4, 5]. he therapy of these infections is oten complicated once many MRSA strains carry multiple genes of antibiotic resistance [6, 7]. he high prevalence of infectious diseases caused by MRSA and other multidrug resistant bacteria has moti- vated the search for new antimicrobial agents and/or new compounds able to potentiate the antimicrobial activity of Hindawi Publishing Corporation BioMed Research International Volume 2014, Article ID 305610, 7 pages http://dx.doi.org/10.1155/2014/305610