Antimicrobial activity of the bioactive components of essential oils from Pakistani spices against Salmonella and other multi-drug resistant bacteria

BACKGROUND The main objective of this study was the phytochemical characterization of four indigenous essential oils obtained from spices and their antibacterial activities against the multidrug resistant clinical and soil isolates prevalent in Pakistan, and ATCC reference strains. METHODS Chemical composition of essential oils from four Pakistani spices cumin (Cuminum cyminum), cinnamon (Cinnamomum verum), cardamom (Amomum subulatum) and clove (Syzygium aromaticum) were analyzed on GC/MS. Their antibacterial activities were investigated by minimum inhibitory concentration (MIC) and Thin-Layer Chromatography-Bioautographic (TLC-Bioautographic) assays against pathogenic strains Salmonella typhi (D1 Vi-positive), Salmonella typhi (G7 Vi-negative), Salmonella paratyphi A, Escherichia coli (SS1), Staphylococcus aureus, Pseudomonas fluorescens and Bacillus licheniformis (ATCC 14580). The data were statistically analyzed by using Analysis of Variance (ANOVA) and Least Significant Difference (LSD) method to find out significant relationship of essential oils biological activities at p <0.05. RESULTS Among all the tested essential oils, oil from the bark of C. verum showed best antibacterial activities against all selected bacterial strains in the MIC assay, especially with 2.9 mg/ml concentration against S. typhi G7 Vi-negative and P. fluorescens strains. TLC-bioautography confirmed the presence of biologically active anti-microbial components in all tested essential oils. P. fluorescens was found susceptible to C. verum essential oil while E. coli SS1 and S. aureus were resistant to C. verum and A. subulatum essential oils, respectively, as determined in bioautography assay. The GC/MS analysis revealed that essential oils of C. cyminum, C. verum, A. subulatum, and S. aromaticum contain 17.2% cuminaldehyde, 4.3% t-cinnamaldehyde, 5.2% eucalyptol and 0.73% eugenol, respectively. CONCLUSIONS Most of the essential oils included in this study possessed good antibacterial activities against selected multi drug resistant clinical and soil bacterial strains. Cinnamaldehyde was identified as the most active antimicrobial component present in the cinnamon essential oil which acted as a strong inhibitory agent in MIC assay against the tested bacteria. The results indicate that essential oils from Pakistani spices can be pursued against multidrug resistant bacteria.