The aim of this study was to evaluate the effect of oregano essential oil, carvacrol and thymol on biofilm-grown Staphylococcus aureus and Staphylococcus epidermidis strains, as well as the effects of the oils on biofilm formation. For most of the S. aureus (n56) and S. epidermidis (n56) strains tested, the biofilm inhibitory concentration (0.125-0.500 %, v/v, for oregano, and 0.031-0.125 %, v/v, for carvacrol and thymol) and biofilm eradication concentration (0.25-1.0 %, v/v, for oregano and 0.125-0.500 %, v/v, for carvacrol and thymol) values were twofold or fourfold greater than the concentration required to inhibit planktonic growth. Subinhibitory concentrations of the oils attenuated biofilm formation of S. aureus and S. epidermidis strains on polystyrene microtitre plates. INTRODUCTIONStaphylococci are important nosocomial pathogens. Eradication of these micro-organisms is not always successful due to their ability to form biofilms. Experimental evidence has shown that micro-organisms in biofilms are less susceptible to conventional treatment (Brown & Gilbert, 1993) than their planktonic counterparts. Many factors contribute to the lowered susceptibility of bacteria enclosed in a biofilm, and include the induction of a biofilm phenotype, the stress response and failure of the antimicrobial agents to penetrate the biofilm (Mah & O'Toole, 2001).As such, alternative strategies or more effective agents exhibiting activity against biofilm-producing micro-organisms are of great interest. Natural drugs could represent an interesting approach to limit the emergence and the spread of these organisms, which currently are difficult to treat. Recently, there has been considerable interest in the study of plant materials as sources of new compounds for processing into therapeutic agents. One approach may be the use of essential oils that have been shown to be potential agents in the treatment of infections, and are safe in terms of human and animal health. In this context, oregano oil and its major phenolic components, carvacrol [2-methyl-5-(1-methylethyl)phenol] and thymol (2-isopropyl-5-methylphenol), are known for their wide spectrum of antimicrobial activity, which has been the subject of several investigations in vitro (Dorman & Deans, 2000;Lambert et al., 2001) and in vivo (Adam et al., 1998;Manohar et al., 2001). They possess multiple biological properties such as anti-inflammatory, anti-leishmanial, antioxidant, hepatoprotective and anti-tumoral activities (Aeschbach et al., 1994; Alam et al., 1999; Robledo et al., 2005;Skold et al., 1998;Weber & de Bont, 1996;Zeytinoglu et al., 2003).Previously, we have shown the efficacy of oregano oil, carvacrol and thymol against planktonic Staphylococcus aureus and Staphylococcus epidermidis, including meticillinresistant strains (Nostro et al., 2004). The objective of this study was to extend the research to evaluate the activity of oregano oil, carvacrol and thymol on biofilm-grown S. aureus and S. epidermidis strains, as well as the effects of oils on biofilm formation....

The aim of this study was to evaluate the susceptibility of methicillin-susceptible and methicillin-resistant staphylococci (MSS, MRS) to oregano essential oil, carvacrol and thymol. The commercial aerial parts of Origanum vulgare L. were hydrodistilled and the essential oil analysed by gas- chromatography/electron impact mass spectrometry. The inhibition efficacy of this essence and its major components was assayed against 26 MSS and 21 MRS, using an agar dilution method. The methicillin resistance was thoroughly typed by Epsilometer test (E-test), polymerase chain reaction for mecA gene detection and PBP2' latex agglutination test. The results clearly demonstrated that the comparison between the susceptibility of MSS and MRS to oregano oil, carvacrol and thymol showed no significant differences (Fisher's exact test, P > 0.05). The best minimum inhibitory concentration values were reported for carvacrol (0.015-0.03%, v/v) followed by thymol (0.03-0.06%, v/v) and oregano oil (0.06-0.125%, v/v).

Epigallocatechin-gallate (EGCg), the major catechin present in green tea extracts, has been shown to have several antibacterial activities, limiting bacterial growth and invasion and acting in synergy with ␤-lactam antibiotics. In this article, we report that EGCg at doses half and below its calculated MIC of 100 g/ml, is able to reverse tetracycline resistance in staphylococcal isolates expressing the specific efflux pump Tet(K) and appears to improve the MICs of tetracycline for susceptible staphylococcal isolates as well. The visible effect of EGCg is an increased accumulation of tetracycline inside bacterial cells. This effect is likely due to the inhibition of pump activity, and it is evident not only for Tet(K) pumps but also for efflux pumps of a different class [Tet(B)]. In summary, our data indicate that the observed dramatic enhancement by EGCg of tetracycline activity for resistant staphylococcal isolates is caused by impairment of tetracycline efflux pump activity and increased intracellular retention of the drug, suggesting a possible use of EGCg as an adjuvant in antibacterial therapy.

Carvacrol is an important component of essential oils and recently has attracted much attention as a result of its biological properties, such as a wide spectrum of antimicrobial activity. The aim of this study was to evaluate the effect of carvacrol in liquid and vapour phase on preformed biofilms of Staphylococcus aureus and Staphylococcus epidermidis by determining biofilm biomass and cultivable cell numbers, and by using epifluorescence and scanning electron microscopy. Carvacrol was able to reduce biofilm biomass and cell viability more effectively when used with liquid contact rather than with vapour phase. The efficacy of treatment with carvacrol vapour was found to be dependent on exposure time. The predominance of red fluorescence using a LIVE/ DEAD BacLight Viability kit (Molecular Probes) and the partially destroyed biofilm architecture as determined by microscopy in treated samples provided evidence for the efficacy of carvacrol. The findings of this investigation suggest a potential application for carvacrol in the inactivation of staphylococcal biofilms. INTRODUCTIONIn recent decades, an increase in the number of staphylococcal infections has been observed worldwide. This has become a clinical and therapeutic problem, as these micro-organisms are resistant to many antimicrobial agents and are a common cause of biofilm-related infections associated with the widespread use of implanted medical devices (O'Gara & Humphreys, 2001;Vuong & Otto, 2002). Poor antimicrobial penetration, nutrient limitation, adaptive stress responses, phenotypic variability and persister-cell formation all contribute towards making biofilm eradication difficult (Hoyle & Costerton, 1991;Mah & O'Toole, 2001).Carvacrol (5-isopropyl-2-methylphenol) is one of the most common components of essential oils. Approved as a safe food additive in the USA and Europe (Center for Food Safety and Applied Nutrition, 2006; Commission of the European Communities, 1999), carvacrol has attracted considerable attention as a result of its wide-spectrum antimicrobial activity, which has been the subject of several investigations (Ben Arfa et al., 2006;Chami et al., 2005;Helander et al., 1998;Lambert et al., 2001;Ultee et al., 1998; Veldhuizen et al., 2006). Carvacrol is effective against bacteria, yeasts, fungi, insects and mites (Ben Arfa et al., It has recently been reported that carvacrol is able to inhibit the growth of preformed biofilm and to interfere with biofilm formation (Knowles & Roller, 2001;Knowles et al., 2005;Nostro et al., 2004). Moreover, a higher antimicrobial activity of carvacrol has been shown using the vapour form compared with solution contact (Burt et al., 2007a;Inouye et al., 2000Inouye et al., , 2001a Inouye et al., , b, 2003Ló pez et al., 2007).The antibacterial activity of carvacrol has been attributed to its hydrophobic nature, the presence of a free hydroxyl group and a delocalized electron system. Carvacrol acts on the cytoplasmic membrane, with considerable effects on the structural and functional properties of the...

Together with VA, NET was the most effective antibiotic tested against both MRSA and MRSE clinical isolates. The exclusive topical use of NET for the treatment of ocular infections may curtail the emergence, spreading and persistence of antibiotic-resistant bacteria.