The battle against multi-resistant strains: Renaissance of antimicrobial essential oils as a promising force to fight hospital-acquired infections

https://doi.org/10.1016/j.jcms.2009.03.017Get rights and content

Summary

Hospital-acquired infections and antibiotic-resistant bacteria continue to be major health concerns worldwide. Particularly problematic is methicillin-resistant Staphylococcus aureus (MRSA) and its ability to cause severe soft tissue, bone or implant infections. First used by the Australian Aborigines, Tea tree oil and Eucalyptus oil (and several other essential oils) have each demonstrated promising efficacy against several bacteria and have been used clinically against multi-resistant strains.

Several common and hospital-acquired bacterial and yeast isolates (6 Staphylococcus strains including MRSA, 4 Streptococcus strains and 3 Candida strains including Candida krusei) were tested for their susceptibility for Eucalyptus, Tea tree, Thyme white, Lavender, Lemon, Lemongrass, Cinnamon, Grapefruit, Clove Bud, Sandalwood, Peppermint, Kunzea and Sage oil with the agar diffusion test. Olive oil, Paraffin oil, Ethanol (70%), Povidone iodine, Chlorhexidine and hydrogen peroxide (H2O2) served as controls.

Large prevailing effective zones of inhibition were observed for Thyme white, Lemon, Lemongrass and Cinnamon oil. The other oils also showed considerable efficacy. Remarkably, almost all tested oils demonstrated efficacy against hospital-acquired isolates and reference strains, whereas Olive and Paraffin oil from the control group produced no inhibition.

As proven in vitro, essential oils represent a cheap and effective antiseptic topical treatment option even for antibiotic-resistant strains as MRSA and antimycotic-resistant Candida species.

Introduction

In recent decades, the incidence of hospital-acquired infections with antibiotic-resistant bacteria has increased remarkably. Notable amongst these infections is methicillin-resistant Staphylococcus aureus (MRSA) (Mulligan et al., 1993, Witte, 1999). MRSA carriers are more likely to have chronic skin lesions requiring multiple admissions, thereby potentially exposing other vulnerable patients (MacKinnon and Allen, 2000, Blok et al., 2001). This leads to significantly increased health care costs, due to the requirement for isolation and sterilization of facilities and instruments used for these patients during their hospital stay. Some hospitals may refuse admission to patients carrying MRSA, thereby compromising their ability to access appropriate health care. Carriage of highly resistant bacterial strains has important epidemiological, financial and logistical implications. Chronic infections with highly resistant strains have a profound effect on individual patients' sense of well-being, comfort, and quality of life (Tonge, 1997, Theaker et al., 2001).

Antibiotic resistance is not the sole domain of bacteria. Many strains of fungi and yeasts are resistant to, or during the course of therapy, develop resistance to antimycotics. Candida species are particularly problematic, as is seen in the example of Candida krusei which has been found frequently to be responsible for multiple drug-resistant opportunistic fungal infections (Pfaller et al., 2008). C. krusei is an extremely important pathogen, particularly in immuno-compromised patients such as transplant recipients and those with acquired-immunodeficiency syndrome (AIDS) (Capoor et al., 2005).

Antibiotic resistance is an evolving problem requiring new strategies to combat infection due to these strains. To date, systemic pharmacological approaches have had varying success. Our current pharmacopoeia is plagued by the development of resistance and by drug toxicity (Wright et al., 1998). Although not yet widely recognized by clinicians, there is mounting international literature evidence supporting the use of plant-derived essential oils against pathogenic microorganisms (Shapiro et al., 1994, Larrondo et al., 1995, Maudsley and Kerr, 1999, Warnke et al., 2004). Both clinical and in vitro studies have demonstrated the potent bactericidal, antimycotic and antifungal properties of some essential oils, including efficacy against antibiotic-resistant strains such as MRSA (Harkenthal et al., 1999, Peana et al., 1999, Halcon and Milkus, 2004). We have previously reported significant clinical utility of essential oils. This included reduction of the malodour caused by head and neck tumour ulceration and promotion of ulcer healing and re-epithelization (Warnke et al., 2004, Warnke et al., 2005, Warnke et al., 2006).

Our aim was to evaluate antibacterial and antimycotic efficacy of different essential oils on frequently isolated and hospital-acquired bacterial strains including MRSA and yeast isolates, including C. krusei, by means of the agar diffusion test.

Section snippets

Test group – essential oils

The following pure essential oils from different countries were selected for analysis: Thyme white oil (Australia), Lemon oil (Nepal), Lemongrass oil (Australia), Cinnamon oil (India), Tea tree oil (Australia), Eucalyptus oil (Australia), Grapefruit oil (Australia), Clove Bud oil (Australia), Lavender oil (France), Peppermint oil (Australia), Sage oil (Germany), Kunzea oil (Australia) and Sandalwood oil (Australia).

All oils were non-diluted and not chemically altered by any solvent or

Results

Test group: with the exception of Sandalwood and Grapefruit oil, all essential oils tested showed good antibacterial and antifungal activity against strains frequently responsible for infections of the oral mucosa and the dermis. The reference strains and also the hospital-acquired isolates were similarly susceptible to the inhibitory effect of the test oils. Inhibition zones had diameters ranging from 7 to 50 mm. The largest effective zones were measured for Thyme white oil (29–36 mm), Lemon oil

Discussion

For hundreds, if not thousands of years, essential oils have been recognized for their therapeutic properties (Halcon and Milkus, 2004). Australian Aborigines used Tea tree oil to treat colds, sore throats, skin infections, and insect bites. Tea tree oil was soon adopted by the white settlers in the country and was sold commercially as a medicinal antiseptic from the early 20th century (Harkenthal et al., 1999). Various studies have demonstrated that essential oils are not only well tolerated,

Acknowledgements

No conflict of interest. No external funding was received for this study.

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