Fig. 2

Antibacterial activity of essential oil evaporative volatile constituents against Gram negative bacteria. Eighteen-hour bacterial broth cultures (Part A: P. aeruginosa (ATCC 35554), Part B: B. bronchiseptica (ATCC 10580), Part C: K. pneumoniae (ATCC 13883)) were used to inoculate TSA petri dishes (1 × 10 cfu/dish). A center plug of agar was removed and a sterile glass cylinder containing increasing amounts of essential oils (0 μL, 10 μL, 20 μL, 40 μL, 80 μL, 160 μL) was placed in the center of the petri dish. Petri dishes were incubated for 24 h at 37 °C. After 24 h of incubation, the zone of inhibition (diameter) was measured. The doses of 0 μL, 10 μL, 20 μL, 40 μL, 80 μL, 160 μL are shown on the graph from light grey to black, respectively. The antimicrobial activity of the essential oil volatiles was divided into six groups based on the zone of inhibition diameter: none (10 mm), negligible (10 mm - 15 mm), low (15 mm - 30 mm), moderate (30 mm - 50 mm), high (50 mm - 70 mm), and highest (70 mm - 80 mm). Error bars indicate the standard deviation from three separate trials. Statistical analysis was performed using a paired t-test. Statistically significant deviation of the various doses compared to untreated was indicated with asterisks: *p = 0.01–0.05; **p = 0.001–0.01; ***p < 0.001