Elsevier

Anaerobe

Volume 17, Issue 6, December 2011, Pages 399-402
Anaerobe

Clinical Microbiology
Antibacterial activities of essential oils from eight Greek aromatic plants against clinical isolates of Staphylococcus aureus

https://doi.org/10.1016/j.anaerobe.2011.03.024Get rights and content

Abstract

Aromatic plants have been used widely to extend the shelf life of foods but at the same time research is undergoes for their properties as antibacterial agents in clinical use. Although there are promising results for the antimicrobial properties of various essential oils against environmental or food-isolated strains of Staphylococcus aureus, limited work has been done concerning these properties against clinical isolates of this pathogen. S. aureus is responsible for an increase number of nosocomial infections and at the same time exhibits increased resistance to synthetic agents.

In this study, essential oils from eight aromatic plants common in Greece were isolated by hydrodistillation, analyzed by gas chromatography (GC) and GC/mass spectrometry (GC/MS) for their chemical components and tested for their antimicrobial activities against 24 clinical isolates of S. aureus. The methods used were disk diffusion and broth dilution in order to determine the Minimum Inhibitory Concentration (MIC).

Our results showed that essential oils from Origanum vulgare and Origanum dictamnus were active against S. aureus when tested by disk diffusion, but exhibited increased MIC values (>256 mg/L) with the dilution method. In contrast, the reference strain NCTC 6571 showed to be extremely sensitive in most of the oils tested (MICs 0.25−32.0 mg/L) and resistant only to the essential oil from Ocimum basilicum. Therefore, there is no evidence of a potential clinical use for those essential oils and further research is needed in order to determine if they could substitute efficiently synthetic antibiotics or, perhaps be used in combination.

Introduction

Essential oils (EO) from aromatic and medicinal plants have been used for many years all over the world either in food processing as flavour enhancers and preservatives or as remedies and cosmetics [1]. In medicine, EOs have been researched for their antibacterial, antifungal, antiviral, insecticidal, anticancer and antioxidant properties [2], [3], [4], [5]. Particularly, the EOs that possess antimicrobial activities have been the subject of many scientific reports resulting in the screening of a wide variety of plant species [6].The main advantage of these natural products is that they do not enhance antibiotic resistance as with the long-term use of synthetic antibiotics [7]. On the other hand, the chemical composition (chemotype) of the EOs which is responsible for the antibacterial properties, is highly depended on various factors like the climatic and geographical conditions as well as harvesting, isolation techniques and storage [8]. These factors interfere in the studies, as the results are influenced by them, thus making difficult the drawing of solid conclusions or comparisons.

One of the most common pathogens causing food poisoning but also frequently responsible for nosocomial infections is Staphylococcus aureus. Particularly, the emergence of antibiotic resistant strains of S. aureus with infection outbreaks among hospitalized patients is a serious problem world wide [9]. Numerous studies have examined the activity of EOs against S. aureus as a foodborne pathogen with promising results [10], [11]. There is evidence of strong inhibition of growth and activity to some metabolic characteristics of food-isolated S. aureus, such as coagulase, lipase and salt tolerant [12]. On the other hand there is a relatively small number of reports focused on clinical isolates of this pathogen and its sensitivity towards the action of EOs [13], [14]. In this study, essential oils from eight aromatic plants common to Greece were isolated by hydrodistillation, analyzed by gas chromatography (GC) and GC/mass spectrometry for their chemical components and tested for their antimicrobial activity against 24 strains of S. aureus isolated from clinical samples.

Section snippets

Clinical strains of S. aureus

Clinical strains of S. aureus were collected from the microbiological laboratories of three major hospitals in Athens (Greece). Most of the strains were isolated from patients with skin infections and some from blood samples and catheters. Initial identification was performed in the hospital laboratories by using their routinely techniques. Strains were transported to our laboratory and if needed they were stored at −30 °C in glycerin contained medium until tested.

Essential oils isolation and chemical composition

Plant parts of Rosmarinus

Chemical composition

Table 1 shows the relative percentage compositions (in major components) isolated from aromatic plants. Linalool was the major component in rosemary (56.6%) and pennyroyal (28.7%), eucalyptol in basil (45.0%), pulegone in spearmint (61.9%), carvone in mint (5.06%), carvacrol in lavender (78.9%) and oregano (43.6%) while menthone (22.6%) and menthol (28.6%) in dictamus. Significant differences between the determined compositions and those published in literature were observed for the above

Discussion

Essential oils from aromatic and medicinal plants have been used for thousands of years from different cultures around the world [2]. Modern science has reveal that some of the essential oils are useful in food preservation [5] and aromatherapy, and also exhibit pharmacological properties such as antibacterial [3], antifungal [18], antioxidant [19], spasmolytic [20], anti-inflammatory and anticancer activities [4]. Such properties can be useful in medicine if the essential oils could

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