Table 1.

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

Organism and no. of isolates	Antibiotic	Fold increase in MIC	Frequency 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
10	RIF	8	8.9 × 10−8	5.9 × 10−8	1.1 × 10−7	7.2 × 10−8	0.0065c
10	MUP	8	7.3 × 10−8	2.3 × 10−8	9.9 × 10−8	3.5 × 10−8	0.0002d
7	VAN	2	2.4 × 10−7	1.2 × 10−7	3.4 × 10−7	5.9 × 10−7	0.1268
4	CIP	2	8.1 × 10−8	5.9 × 10−8	8.6 × 10−8	3.7 × 10−8	0.6725
E. coli
10	RIF	8	3.7 × 10−8	2.9 × 10−8	4.3 × 10−8	3.8 × 10−8	0.2083
9	KAN	2	3.3 × 10−6	2.0 × 10−7	2.6 × 10−6	3.1 × 10−7	<0.0001e

^aValues are the geometric means from 4 to 10 isolates. MUP, mupirocin; RIF, rifampin; VAN, vancomycin; CIP, ciprofloxacin; KAN, kanamycin; TTO, tea tree oil.

^bP values were obtained by repeated-measure one-way ANOVA.

^cSignificant differences exist between treatments B and C (P < 0.01) (Bonferroni post test).

^dSignificant differences exist between treatments A and B (P < 0.01), B and C (P < 0.001), and C and D (P < 0.05).

^eSignificant 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).