Frequencies of resistance to Melaleuca alternifolia (tea tree) oil and rifampicin in Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecalis.
This study was conducted to determine the frequencies at which single-step mutants resistant to tea tree oil and rifampicin occurred amongst the Gram-positive organisms Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecalis. For tea tree oil, resistance frequencies were very low at <10(-9). Single-step mutants resistant to tea tree oil were undetectable at two times the minimum inhibitory concentration (MIC) for S. aureus RN4220 and derivative mutator strains or at 3 x MIC for the remaining S. aureus strains, including a clinical meticillin-resistant S. aureus isolate. Similarly, no mutants were recovered at 2x MIC for S. epidermidis or at 1x MIC for E. faecalis. Resistance frequencies determined in vitro for rifampicin (8 x MIC) ranged from 10(-7) to 10(-8) for all isolates, with the exception of the S. aureus mutator strains, which had slightly higher frequencies. These data suggest that Gram-positive organisms such as Staphylococcus and Enterococcus spp. have very low frequencies of resistance to tea tree oil.
Hammer
Katherine A
KA
Discipline of Microbiology and Immunology, School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA, Australia. khammer@cyllene.uwa.edu.au
Carson
Christine F
CF
Riley
Thomas V
TV
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000235:genetics; D013293:Enterococcus faecalis / Q000187:drug effects / Q000235:genetics; D006095:Gram-Positive Cocci / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D031650:Melaleuca / Q000737:chemistry; D008826:Microbial Sensitivity Tests; D009154:Mutation; D012293:Rifampin / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects / Q000235:genetics; D013212:Staphylococcus epidermidis / Q000187:drug effects / Q000235:genetics; D020947:Tea Tree Oil / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D020947:Tea Tree Oil; D012293:Rifampin