Satureja hortensis L. essential oil causes Acinetobacter baumannii membrane disruption

Essential oils are promising antimicrobial agents against various bacteria, including Acinetobacter baumannii , a highly resistant clinical opportunistic pathogen with an increasing prevalence. The traditional application of the aromatic and medicinal plant Satureja hortensis L. (Lamiaceae) as a natural remedy for the treatment of inflammatory diseases, nausea, diarrhea, and various infectious diseases is well known. The aim of the study was to determine the antimicrobial activity and potential target site for S. hortensis essential oil against A. baumannii . The effect of the essential oil was determined using the microdilution broth method. The determined minimal inhibitory concentration (MIC=1 µl mL -1 ) showed that S. hortensis essential oil possesses a significant anti- A. baumannii effect. The A. baumannii reference strain ATCC 19606 cells in the exponential growth phase were treated for 3 h at 37 °C with MIC of S. hotensis essential oil and examined by scanning electron microscopy. The electron micrographs highlighted the occurrence of collapsed cells with perforations, cell content leakage, cell debris, but also cell autoaggregation (Fig. 1B). The autoaggregation was further confirmed by an autoaggregation test: untreated cells (Fig. 1A) were partially autoaggregative, while the treated cells were highly autoaggregative, as a result of changes of the cell surface properties. Thus, the essential oil affected the membrane systems of A. baumannii cells, causing structural changes of the bacterial cells. Since A. baumannii strains are susceptible to S. hortensis essential oil, the oil possesses a great potential in the control of growth of this species.