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