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Influence of Origanum vulgare L. essential oil on enterotoxin production, membrane permeability and surface characteristics of Staphylococcus aureus

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Abstract

This study evaluated the influence of the essential oil from Origanum vulgare L. on the enterotoxin production, membrane permeability and cell surface characteristics of Staphylococcus aureus. The suppression of enterotoxin production occurred totally in the broth added with the essential oil at subinhibitory concentrations (0.3 and 0.15 µL/mL). Loss of 260-nm-absorbing material and potassium ions occurred immediately after addition of the essential oil at 0.6 and 1.2 µL/mL and followed up to 120 min. Electron microscopy of essential oil-treated cells revealed the formation of roles in the cell surfaces and loss of cytoplasm material. According to these results, O. vulgare essential oil could be rationally applied in food products both to inhibit the growth of S. aureus and to suppress the synthesis of staphylococcal enterotoxins.

Introduction

Staphylococcus aureus is considered the third most important cause of disease in the world among the reported foodborne illnesses (Acco et al., 2003, Boerema et al., 2006). The growth of S. aureus in food presents a potential public health hazard because many strains produce one or most enterotoxins (SEs) that cause food poisoning if ingested (Akineden et al., 2008, Bania et al., 2006). Even though foodborne S. aureus poisoning is a mild and generally self-limiting disease, the disease poses a considerable social burden in terms of hospital expenses, loss of patients' working days and productivity (Normanno et al., 2005, Normanno et al., 2007).

Since staphylococcal foodborne intoxication poses a threat for human health worldwide, the development of strategies to control the survival and growth of S. aureus in food has been of great interest (Souza et al., 2009). Consumers currently have demanded for safe and more natural food with small amount of chemical preservatives. This trend prompts a particular increased interest in the use of essential oils as antimicrobial compounds to be applied in food conservation (Marino et al., 2001, Skandamis et al., 2002).

Previous studies showed that Origanum vulgare L. essential oil possesses broad-spectrum antimicrobial activity (Chun et al., 2005, Nostro et al., 2004, Souza et al., 2007). The essential oil from O. vulgare is a complex mixture containing lipophilic monoterpenes, of which carvacrol and thymol are believed to be responsible for its antimicrobial properties (Lambert et al., 2001, Rhayour et al., 2003). In a previous study we found that O. vulgare essential oil strongly inhibited the growth and some metabolic characteristics of food-isolated S. aureus strains, including the activity of coagulase, lipase and salt tolerance (Barros et al., 2009). Here we report the further investigation of the anti-staphylococcal properties of O. vulgare essential oil, particularly its influence on enterotoxins production, membrane permeability and surface characteristics of S. aureus.

Section snippets

Test organisms

S. aureus QCF obtained from the Microorganism Collection, Laboratory of Food Microbiology, Health Sciences Center, Federal University of Paraíba, João Pessoa, Brazil was used as test strain in all experiments. This strain was isolated from an unripened cheese sample by the standard procedures (Bennett et al., 1986, Vanderzant and Splittstoesser, 1992). Stock culture was kept on Nutrient Agar — NA (Sigma, France) slant under refrigeration (7 °C ± 1 °C).

Inocula used in the assays were obtained from

Enterotoxin production

The O. vulgare essential oil assayed here showed previously Minimum Inhibitory Concentration and Minimum Bactericidal Concentration of 0.6 and 1.2 µL/mL, respectively, against S. aureus QCF (Souza et al., 2009). The influence of O. vulgare essential oil at subinhibitory concentrations on the enterotoxins production by S. aureus QCF was evaluated (Table 1). Growth of S. aureus in the presence of the essential oil at 0.3 and 0.15 µL/mL caused total inhibition of the enterotoxins production.

Loss of 260-nm-absorbing material and release of potassium ions

The

Discussion

Effect of the essential oil from O. vulgare on the enterotoxins production, membrane permeability and surface characteristics of S. aureus was reported. For all observed parameters, the essential oil interfered with physiological characteristics and microbial morphogenesis in a dose-dependent manner.

Assays of enterotoxins revealed that the essential oil from O. vulgare at subinhibitory concentrations suppressed the production of staphylococcal enterotoxins. This phenotypic change possibly

Acknowledgments

The authors thank to CNPq (Conselho Nacional de Desenvolvimento Científico e Technológico, Brazil) for the financial support.

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