Table 3

Summary of E. coli MICs of antibiotics (μg/ml) alone, antibiotics with tea tree oil (0.062%) or terpinen-4-ol (0.031%), and tea tree oil or terpinen-4-ol without antibiotics, determined by serial subculturea

Agent (no. of isolates) and parameterTreatmentMIC on day:
123456
CIP (12)
    MedianAlone0.0080.0160.0160.030.030.12
With TTO0.0080.0160.030.060.060.12
With T4ol0.0080.0160.060.060.120.12
    GMAlone0.0100.0250.0340.0700.0700.140
With TTO0.0070.0140.0290.0450.0640.122
With T4ol0.0090.0180.0480.0780.1000.147
KAN (11)
    MedianAlone832166464128
With TTO41632323264
+With T4ol41632323264
    GMAlone6.745.320.260.450.8107.6
With TTO4.812.733.938.142.747.9
With T4ol2.515.128.533.932.053.8
AMP (10)
    MedianAlone24881616
With TTO24881616
With T4ol24881632
    GMAlone2.14.98.010.611.316.0
With TTO2.14.68.69.812.112.1
With T4ol2.14.911.311.317.124.3
Tea tree oil (18)
    MedianAlone0.511111
    GMAlone0.650.730.961.001.120.96
Terpinen-4-ol (18)
    MedianAlone0.120.250.250.250.250.25
    GMAlone0.130.170.220.290.250.26
  • a GM, geometric means. Boldface type indicates that the MIC is more than double the baseline (day 1) value. Single underlining indicates that values differed significantly from antibiotic alone on that day. Double underlining indicates significant differences between tea tree oil and terpinen-4ol treatments on that day.