Phytomedicine 20 (2013) 432–435 Contents lists available at SciVerse ScienceDirect Phytomedicine jou rn al hom epage: www.elsevier.de/phymed Short communication Synergistic interactions of epigallocatechin gallate and oxytetracycline against various drug resistant Staphylococcus aureus strains in vitro Pavel Novy a , Johana Rondevaldova b , Lenka Kourimska a , Ladislav Kokoska b,∗ a Department of Quality of Agricultural Products, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Kamycka 129, 165 21 Prague 6 – Suchdol, Czech Republic b Department of Crop Sciences and Agroforestry, Institute of Tropics and Subtropics, Czech University of Life Sciences Prague, Kamycka 129, 165 21 Prague 6 – Suchdol, Czech Republic a r t i c l e i n f o Keywords: Staphylococcus aureus Epigallocatechin gallate Oxytetracycline Antimicrobial Resistance Synergy a b s t r a c t Epigallocatechin gallate (EGCG), the major catechin contained in tea leaves, is known to possess the syn- ergistic anti-staphylococcal activity in combination with various -lactam antibiotics and tetracycline. In the present study, we explored the in vitro combinatory effect of EGCG in combination with oxytetracy- cline against eight standard strains and clinical isolates of Staphylococcus aureus, including erythromycin, methicillin and tetracycline resistant strains. The minimum inhibitory concentrations were determined by the broth microdilution assay and the data were evaluated according to the sum of fractional inhibitory concentrations ( ∑ FIC). Our results showed synergistic and additive interactions against all S. aureus strains tested ( ∑ FIC 0.288–0.631), two of which were multidrug resistant. According to our best knowl- edge, it is the first report on the EGCG synergy with oxytetracycline. Considering its significant synergistic antimicrobial effect and low toxicity, we suggest EGCG as a promising compound for the development of new anti-staphylococcal formulations. © 2013 Elsevier GmbH. All rights reserved. Introduction The bacterial resistance is a phenomenon inevitably connected with the use of antimicrobials (French 2010). It has become the major global problem in the treatment of infectious diseases, thus creating a continuous need for new therapeutic options (Jordheim et al. 2012). Among bacterial pathogens, Staphylococ- cus aureus is one of the most serious ones due to its potential for rapid acquisition of drug resistance (French 2010). One of the recently adopted strategies for fast development of new antimi- crobials effective against resistant pathogens is the combination of approved drugs (Jordheim et al. 2012). Another option to over- come the bacterial resistance is the combination of currently used antibiotics with compounds derived from plants tradition- ally used by humans for food or medicinal purposes (Wagner and Ulrich-Merzenich 2009). Epigallocatechin gallate (EGCG) (Fig. 1), the major catechin contained in tea [Camellia sinensis (L.) Kuntze] leaves, is an example of such a kind of synergistically acting antimicrobial agent. Besides the recent report on its synergy with imipenem against Klebsiella pneumoniae (Cho et al. 2011) it has been reported to potentiate the anticandidal effect of ampho- tericin B (Hirasawa and Takada 2004) and the activity of -lactams ∗ Corresponding author. Tel.: +420 224382180; fax: +420 234381829. E-mail address: kokoska@its.czu.cz (L. Kokoska). and tetracycline against methicillin and tetracycline resistant S. aureus, respectively (Abreu et al. 2012). This anti-staphylococcal activity is attributed to the EGCG effect on the bacterial cell wall (Zhao et al. 2001), inhibition of penicillinase activity (Zhao et al. 2002), and inhibition of tetracycline efflux (Roccaro et al. 2004). Despite the fact that the ability of EGCG to effectively increase the anti-staphylococcal effect of tetracycline has previously been described, its interaction with other tetracycline antibiotics has poorly been studied. Therefore, we decided to evaluate the in vitro synergistic effect of EGCG with oxytetracycline, a combination selected as the most promising result of the initial screening of EGCG with representatives of eight major antibiotic classes (Novy et al. 2009), against various drug resistant strains of S. aureus. Materials and methods Chemicals Bacteria were grown in cation adjusted Mueller-Hinton broth (MHB; Oxoid, Basingstoke, UK). Tris-buffered saline used for the MHB equilibration was purchased from Sigma–Aldrich (Prague, CZ) as well as the antimicrobials tested: EGCG, oxacillin and oxytetracycline. Dimethyl sulfoxid, hydrochloric acid (Lach-Ner, Neratovice, CZ) and deionised water were used as solvents. 0944-7113/$ – see front matter © 2013 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.phymed.2012.12.010