Antimicrobial activity, cytotoxicity and chemical analysis of lemongrass essential oil (Cymbopogon flexuosus) and pure citral

Abstract

The aim of this study was to determine the antimicrobial effects of lemongrass essential oil (C. flexuosus) and to determine cytotoxic effects of both test compounds on human dermal fibroblasts. Antimicrobial susceptibility screening was carried out using the disk diffusion method. Antimicrobial resistance was observed in four of five Acinetobacter baumannii strains with two strains confirmed as multi-drug-resistant (MDR). All the strains tested were susceptible to both lemongrass and citral with zones of inhibition varying between 17 to 80 mm. The mean minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of citral (mic-0.14 % and mbc-0.3 % v/v) was lower than that of Lemongrass (mic-0.65 % and mbc-1.1 % v/v) determined using the microtitre plate method. Cell viability using human dermal fibroblasts (HDF; 106-05a) was determined following exposure to both compounds and a control (Grapeseed oil) using the XTT assay and the IC₅₀ determined at 0.095 % (v/v) for citral and 0.126 % (v/v) for lemongrass. Grapeseed oil had no effect on cell viability. Live cell imaging was performed using the LumaScope 500 imaging equipment and changes in HDF cell morphology such as necrotic features and shrinkage were observed. The ability of lemongrass essential oil (EO) and citral to inhibit and kill MDR A. baumannii highlights its potential for use in the management of drug-resistant infections; however, in vitro cytotoxicity does suggest further tests are needed before in vivo or ex vivo human exposure.

Keywords: Acinetobacter baumannii; IC50; Lemongrass oil; Multi-drug resistance (MDR); Toxicity.

Fig. 1

Comparison of the inhibition zones (mm) of whole lemongrass EO (black bars) and citral (grey bars) against A. baumannii isolates measured on agar medium. **The disk diffusion of ATCC® BAA-1709™ is significantly different from the other isolates (P = 0.02). When the disk diffusion of the other four isolates were compared, there was no significant difference (P = 0.25)

Fig. 2

Dose-dependent cytotoxicity calculated as the relative cell viability (%) of whole lemongrass EO, citral and grapeseed EO (carrier oil) on HDF as determined by the XTT assay. Each experiment was performed in quadruplicate on four separate occasions. Grapeseed oil was also performed in quadruplicate and repeated on two separate occasions

Fig. 3

Human dermal fibroblasts (HDF; 106-05a) obtained from ECACC grown to 80 % confluence using the DMEM medium and supplemented with 10 % (v/v) FBS and 1 % (v/v) Gibco® GlutaMAX™ prior to treatment with test compounds. ×40 objective

Fig. 4

Cellular morphology changes of the HDF cells exposed to Lemongrass EO (C. flexuosus) at 1 % (v/v) and citral at 0.25 % (v/v) over a 2-h period. The images shown represent images captured at 1, 10, 30 and 60 min, respectively, using the LumaScope 500. ×40 objective