Tea Tree Oil and Antibiotic Resistance TABLE 4 MICs of antibiotics (ug/ml),biocides (ug/ml),and tea tree oil and terpinen-4-ol (%vol/vol)for three Staphylococcus strains serially subcultured with terpinen-4-ol or tea tree oil S.aureus NCTC 6571 S.aureus ATCC 25923 S.epidermidis ATCC 12228 MIC MIC MIC With 0.1% With 0.1% With 0.1% With 0.2% Agent Passage no. Control T4ol Passage no. Control T4ol TTO Passage no. Control T4ol AMX 19 0.12 0.06 18 0.12 0.12 0.12 14 0.5 22 0.25 0.25 0.5 0.25 17 1 0.5 CIP 17 0.25 0.06 公 0.12 0.12 0.25 1g 0.25 0.25 19 0.12 0.06 18 0.25 0.06 0.12 17 0.5 0.25 22 0.12 0.06 20 0.25 0.06 Downloaded GEN 1> 16 0.5 0.25 0.5 14 0.12 0.5 19 0.25 0.12 0.12 0.25 0.25 22 20 0.25 0.25 from TET 17 0.12 0.06 0.12 0.12 0.25 4 0. 0.5 19 0.25 <0.03 18 0.25 0.12 0.25 17 0.5 22 0.12 0.06 20 0.25 0.12 http://aac. VAN 1 16 2 4 19 1 0.5 18 22 0.5 0.25 20 1 .asm.org/ Benzalkonium ◇ 0.5 16 2 0.5 Chloride 19 1 18 2 0.5 2 1 20 2 0.5 May Triclosan 19 0.06 0.03 18 0.06 0.03 0.03 0.03 0.06 22 0.12 0.12 20 0.25 0.12 Tea tree oil 17 0.5 0.25 16 0.12 0.25 0.25 0.5 19 1 0.5 18 0.5 0.5 0.5 17 0.5 0.5 22 0.25 0.25 20 0.5 0.5 Terpinen-4-ol 17 0.25 0.5 16 0.25 0.5 0.5 14 0.5 0.5 19 0.5 0.5 18 0.5 0.5 0.25 17 0.5 0.5 SHAN 22 0.12 0.25 20 0.12 0.25 Boldface type indicates a difference in MIC of 4-fold or more for passaged and nonpassaged strains 工 delaying the development of antibiotic resistance(22,27).One of affected by either culturing with tea tree oil or combining antibi- the best known is the treatment of tuberculosis with combinations otic with tea tree oil.The exception was kanamycin,whereby E. of rifampin,isoniazid,pyrazinamide,and ethambutol(19,29).At coliresistance frequencies were consistently approximately 1 logo the other end of the spectrum,there are concerns that the overuse lower when cultured on kanamycin agar with tea tree oil for both of antimicrobial agents such as biocides leads to increases in anti- control cultures and tea tree oil cultures.Culturing with tea tree oil ① biotic resistance (15).These concerns relate to the use of disinfec- prior to determining resistance frequencies had no significant im- tants and antiseptics in the domestic environment and the theory pact.Two possible explanations for the differences in resistance that the increased and chronic exposure of bacteria to sublethal frequencies are that the tea tree oil is preventing mutations(and n concentrations of biocide leads to tolerance,which may also con- decreasing the overall mutation rate)or decreasing the survival of fer tolerance to antibiotics.Since several biocides have multiple, a small proportion of resistant mutants (no change in mutation nonspecific mechanisms of action,similarly to tea tree oil,this rate).There is little evidence to support the first possibility,since same concern could apply to the oil.Although decreased antibi- (i)if this was the case we would expect more differences in muta- otic susceptibility following biocide exposure has been demon- tion rates in the current study,and (ii)previous studies have strated in vitro(4,16),there isstill debate as to what impact,ifany, shown that tea tree oil neither increases(12,14)nor decreases(12) this has in clinical practice(17).The current study has demon- mutations using the bacterial reverse mutation assay.This there- strated that tea tree oil has little impact on the development of fore suggests that the decreased number of mutants is specific to antibiotic resistance,and that exposure to the major component kanamycin and its mechanism(s)of action and resistance.Amin- terpinen-4-ol does not significantly alter antimicrobial suscepti- oglycosides exert antibacterial action primarily by interfering with bility. protein synthesis by binding to rRNA in the small subunit of the Frequencies ofsingle-step antibiotic resistance were largely un- pacterial ribosome.Mechanisms of kanamycin resistance include February 2012 Volume 56 Number 2 aac.asm.org 913delaying the development of antibiotic resistance (22, 27). One of the best known is the treatment of tuberculosis with combinations of rifampin, isoniazid, pyrazinamide, and ethambutol (19, 29). At the other end of the spectrum, there are concerns that the overuse of antimicrobial agents such as biocides leads to increases in anti￾biotic resistance (15). These concerns relate to the use of disinfec￾tants and antiseptics in the domestic environment and the theory that the increased and chronic exposure of bacteria to sublethal concentrations of biocide leads to tolerance, which may also con￾fer tolerance to antibiotics. Since several biocides have multiple, nonspecific mechanisms of action, similarly to tea tree oil, this same concern could apply to the oil. Although decreased antibi￾otic susceptibility following biocide exposure has been demon￾strated in vitro (4, 16), there is still debate as to what impact, if any, this has in clinical practice (17). The current study has demon￾strated that tea tree oil has little impact on the development of antibiotic resistance, and that exposure to the major component terpinen-4-ol does not significantly alter antimicrobial suscepti￾bility. Frequencies of single-step antibiotic resistance were largely un￾affected by either culturing with tea tree oil or combining antibi￾otic with tea tree oil. The exception was kanamycin, whereby E. coli resistance frequencies were consistently approximately 1 log10 lower when cultured on kanamycin agar with tea tree oil for both control cultures and tea tree oil cultures. Culturing with tea tree oil prior to determining resistance frequencies had no significant im￾pact. Two possible explanations for the differences in resistance frequencies are that the tea tree oil is preventing mutations (and decreasing the overall mutation rate) or decreasing the survival of a small proportion of resistant mutants (no change in mutation rate). There is little evidence to support the first possibility, since (i) if this was the case we would expect more differences in muta￾tion rates in the current study, and (ii) previous studies have shown that tea tree oil neither increases (12, 14) nor decreases (12) mutations using the bacterial reverse mutation assay. This there￾fore suggests that the decreased number of mutants is specific to kanamycin and its mechanism(s) of action and resistance. Amin￾oglycosides exert antibacterial action primarily by interfering with protein synthesis by binding to rRNA in the small subunit of the bacterial ribosome. Mechanisms of kanamycin resistance include TABLE 4 MICs of antibiotics (g/ml), biocides (g/ml), and tea tree oil and terpinen-4-ol (%, vol/vol) for three Staphylococcus strains serially subcultured with terpinen-4-ol or tea tree oila Agent S. aureus NCTC 6571 S. aureus ATCC 25923 S. epidermidis ATCC 12228 Passage no. MIC Passage no. MIC Passage no. MIC Control With 0.1% T4ol Control With 0.1% T4ol With 0.1% TTO Control With 0.2% T4ol AMX 19 0.12 0.06 18 0.12 0.12 0.12 14 1 0.5 22 0.25 0.25 20 0.5 0.25 17 1 0.5 CIP 17 0.25 0.06 16 0.12 0.12 0.25 14 0.25 0.25 19 0.12 0.06 18 0.25 0.06 0.12 17 0.5 0.25 22 0.12 0.06 20 0.25 0.06 GEN 17 1 2 16 0.5 0.25 0.5 14 0.12 0.5 19 1 1 18 0.25 0.12 0.12 17 0.25 0.25 22 1 2 20 0.25 0.25 TET 17 0.12 0.06 16 0.12 0.12 0.25 14 0.5 0.5 19 0.25 0.03 18 0.25 0.12 0.25 17 1 0.5 22 0.12 0.06 20 0.25 0.12 VAN 17 1 1 16 2 2 2 14 4 4 19 1 0.5 18 1 1 2 17 4 4 22 0.5 0.25 20 1 1 Benzalkonium 17 0.5 1 16 2 0.5 2 14 2 1 Chloride 19 1 1 18 2 0.5 1 17 2 1 22 1 1 20 2 0.5 Triclosan 19 0.06 0.03 18 0.06 0.03 0.03 17 0.03 0.06 22 0.12 0.12 20 0.25 0.12 Tea tree oil 17 0.5 0.25 16 0.12 0.25 0.25 14 0.5 0.5 19 1 0.5 18 0.5 0.5 0.5 17 0.5 0.5 22 0.25 0.25 20 0.5 0.5 Terpinen-4-ol 17 0.25 0.5 16 0.25 0.5 0.5 14 0.5 0.5 19 0.5 0.5 18 0.5 0.5 0.25 17 0.5 0.5 22 0.12 0.25 20 0.12 0.25 a Boldface type indicates a difference in MIC of 4-fold or more for passaged and nonpassaged strains. Tea Tree Oil and Antibiotic Resistance February 2012 Volume 56 Number 2 aac.asm.org 913 on May 12, 2015 by SHANGHAI JIAOTONG UNIVERSITY http://aac.asm.org/ Downloaded from