Table 1

Frequencies of single-step antibiotic-resistant mutants occurring in the presence and absence of tea tree oila

Organism and no. of isolatesAntibioticFold increase in MICFrequency of mutants in:P valueb
Control culture with:TTO culture with:
Antibiotic alone (treatment A)Antibiotic + TTO (treatment B)Antibiotic alone (treatment C)Antibiotic + TTO (treatment D)
S. aureus
    10RIF88.9 × 10−85.9 × 10−81.1 × 10−77.2 × 10−80.0065c
    10MUP87.3 × 10−82.3 × 10−89.9 × 10−83.5 × 10−80.0002d
    7VAN22.4 × 10−71.2 × 10−73.4 × 10−75.9 × 10−70.1268
    4CIP28.1 × 10−85.9 × 10−88.6 × 10−83.7 × 10−80.6725
E. coli
    10RIF83.7 × 10−82.9 × 10−84.3 × 10−83.8 × 10−80.2083
    9KAN23.3 × 10−62.0 × 10−72.6 × 10−63.1 × 10−7<0.0001e
  • a Values are the geometric means from 4 to 10 isolates. MUP, mupirocin; RIF, rifampin; VAN, vancomycin; CIP, ciprofloxacin; KAN, kanamycin; TTO, tea tree oil.

  • b P values were obtained by repeated-measure one-way ANOVA.

  • c Significant differences exist between treatments B and C (P < 0.01) (Bonferroni post test).

  • d Significant differences exist between treatments A and B (P < 0.01), B and C (P < 0.001), and C and D (P < 0.05).

  • e Significant differences exist between treatments A and B (P < 0.001), A and D (P < 0.01), B and C (P < 0.001), and C and D (P < 0.01).