Assessment of the antipeudomonal activity of three essential oils using flow cytometry approach

Abstract

Beside its rapidity, flow cytometry is a very sensitive technique allowing both the detection of dead, metabolically active, viable and viable but no-cultivable cells. This approach was used, in this work, to estimate the antibacterial activity of essential oils (EO) from three aromatic herbs: Mentha spicata (MS), Mentha pulegium, and Rosmarinus officinalis against Pseudomonas aeruginosa ATCC 27853, which is an opportunist and food spoilage bacteria. The functional damages induced in P. aeruginosa treated with the three oils and incubated at 4 °C, 7 °C and 37°C was assessed and growth of tested strain was followed over time together with Suber green, Propidium iodide and ChemChrome V6. Irrespective of the culture conditions (the tested oil, its concentration, the time and the incubation temperature), significant reduction rate was observed compared with control, but there was generally no significant difference between the effects of all oils. In fact, after 10 h of incubation at 37°C, the total population in the treated inoculums with EO of Mentha pulegium at 0.4% concentration was 4 times lower than control preparation. At 7°C, metabolically active bacteria in the inoculums without treatment represented 25.65% on the 5th day, dropped to 12% on 10th day, then increase to the 37% on the 21st day. Whereas, the percentage of those treated was around 13, 10 and 15%, on the 5th, 10th and 21st day, respectively. We have noted that the incubation at 4 °C leaded to the stress of the cells with or without oils and the percentage of active cells was less or equal 8 % at the 21st day.