Positive Health Online

Abstract

GUSTAFSON and colleagues, Microbiology Group, School of Biomedical Sciences, Curtin University of Technology, Perth, Western Australia, studied the bactericidal actions of tea tree oil (TTO) on antibiotic-resistant (mutant) strains of Escherichia coli (E coli).

Background

Methodology

The investigators compared the antibacterial actions of TTO in vitro on the parent strain of E coli (AG100) and on mutants of the parent strain demonstrating the multiple antibiotic resistance (Mar) phenotype . The researchers also attempted to isolate Mar mutants of Staphylococcus aureus using tetracycline gradients; however, this was unsuccessful. The bactericidal actions of TTO against S aureus strain BB255 grown in the presence or absence of salicylate were compared.

Results

Mutant E coli strains exhibiting the Mar phenotype were found to be more resistant to the killing action of TTO compared with the parent strain. TTO's bactericidal actions were greater at 37oC than at 30oC for all E. coli strains studied. Parent strain E coli showed increased tolerance to TTO when grown in the presence of salicylate, which is known to induce the mar operon leading to the Mar phenotype. The killing actions of antimicrobial terpines found in TTO were reduced in E coli Mar mutant YL1 in comparison with parent strain AG100. S aureus strain BB255 was more resistant to TTO when grown in the presence of salicylate than in its absence.

Conclusion

Bacterial Mar phenotypes increase resistance to the bactericidal action of TTO . The results also suggest that TTO's site of action is the bacterial cell membrane .

References

Gustafson JE et al. The bacterial multiple antibiotic resistant (Mar) phenotype leads to increased tolerance to tea tree oil. Pathology 33 (2): 211-5. May 2001.