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. 2018 Oct 9;23(10):2584.
doi: 10.3390/molecules23102584.

High Potency of Melaleuca alternifolia Essential Oil against Multi-Drug Resistant Gram-Negative Bacteria and Methicillin-Resistant Staphylococcus aureus

Alessandra Oliva  1 , Silvia Costantini  2 , Massimiliano De Angelis  3 , Stefania Garzoli  4 , Mijat Božović  5 , Maria Teresa Mascellino  6 , Vincenzo Vullo  7 , Rino Ragno  8   9
Affiliations

High Potency of Melaleuca alternifolia Essential Oil against Multi-Drug Resistant Gram-Negative Bacteria and Methicillin-Resistant Staphylococcus aureus

Alessandra Oliva et al. Molecules. .

Abstract

Purpose: Herein, an extended investigation of Tea tree oil (TTO) against a number of multi-drug resistant (MDR) microorganisms in liquid and vapor phases is reported.

Methods: The activity of TTO was tested against methicillin-sensitive Staphylococcus aureus (MSSA), Escherichia coli, and clinical strains of methicillin-resistant S. aureus (MRSA), extended-spectrum beta lactamases producer carbapenem-sensitive Klebsiella pneumoniae (ESBL-CS-Kp), carbapenem-resistant K. pneumoniae (CR-Kp), Acinetobacter baumannii (CR-Ab), and Pseudomonas aeruginosa (CR-Pa). Minimal inhibitory/bactericidal concentrations (MIC/MBCs) and synergistic activity between TTO and different antimicrobials were determined. In the vapor assay (VP), TTO-impregnated discs were placed on the lid of a petri dish and incubated for 24 h at 37 °C.

Results: TTO showed a potent bactericidal activity against all the tested microorganisms. TTO in combination with each reference antimicrobial showed a high level of synergism at sub-inhibitory concentrations, particularly with oxacillin (OXA) against MRSA. The VP assay showed high activity of TTO against CR-Ab.

Conclusion: Evaluation of in-vitro activity clearly indicated TTO as a potential effective antimicrobial treatment either alone or in association with known drugs against MDR. Therefore, TTO could represent the basis for a possible role in non-conventional regimens against S. aureus and Gram-negative MDR. TTO in VP might represent a promising option for local therapy of pneumonia caused by CR-Ab.

Keywords: Melaleuca alternifolia; carbapenem-resistant microorganisms; essential oils; methicillin-resistant Staphylococcus aureus; multi-drug resistant bacteria.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Disk diffusion (panel A) and vapor phase (panel B) activity of TTO. MSSA: Methicillin-susceptibility Staphylococcus aureus; MRSA: Methicillin-resistant Staphylococcus aureus; ESBL: Extended Spectrum Beta-Lactamases; CS: Carbapenem-Susceptible; CR: Carbapenem-Resistant; Kp: Klebsiella pneumoniae; Ab: Acinetobacter baumannii; Pa: Pseudomonas aeruginosa.
Figure 2
Figure 2
Activity of TTO against MRSA at different concentrations throughout killing study. GC: Growth Control; MRSA: Methicillin-resistant Staphylococcus aureus. Dashed line represents bactericidal activity.
Figure 3
Figure 3
Activity of TTO (v/v) and OXA (μg/mL) at different concentrations against MRSA throughout killing study. GC: Growth Control; MRSA: Methicillin-resistant Staphylococcus aureus; OXA: oxacillin. Dashed line represents bactericidal activity.
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