Antimicrobial activity of bioactive components of essential oils from Citrus sinensis against important pathogens

Alternative strategies to treat multidrug resistant pathogens are indispensable due to the scarcity of new therapeutically effective antibiotics. The present work was conducted to investigate the antimicrobial effects of essential oils extracted from Citrus sinensis, locally known as “Mousami”, against various important pathogens as well as their phytochemical characterisation. Essential oils were extracted from Cit. sinensis peels by the steam distillation method, and a 0.23% yield was obtained. Chemical composition of the extracted essential oil was analysed through gas chromatography/mass spectrometry (GC/MS). The analysis revealed that the Cit. sinensis essential oil was composed of a variety of chemical compounds; mostly are monoterpene hydrocarbon and 0.62% of limonene (dipentene), as well as oxygenated monoterpenes and 0.50% limonene oxide, also known as eucalyptol. Standard reference microorganisms, i.e., E. coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), Salmonella Typhi (ATCC 24682), Bacillus subtilis (ATCC 6633), Aspergillus flavus (ATCC 204304), and Candida albicans (ATCC 10231) were used, and the in vitro antimicrobial effect of Cit. sinensis essential oils was observed against these strains by disc diffusion method. Statistical analysis of the resulting data was done by using Least Significant Difference (LSD) method and Analysis of Variance (ANOVA) to assess the significant association between biological activities of essential oils at p < 0.05. Using microbroth dilution assay, maximum sensitivity was exhibited by E. coli and Can. albicans among the tested microbial strains. The zones of inhibition were significantly different, having diameters of 34.0 ± 1.5 and 55.0 ± 0.5 mm for the said bacterial and fungal strains, respectively; and their MIC values were 0.0007 ± 0.0001 and 0.0007 ± 0.0006 mg/ml, respectively. Thin layer chromatography-bioautography (TLC-bioautography) showed dipentene as biologically most active antimicrobial component. Hence, it was established that broad spectrum antimicrobial effect against important microorganisms was elucidated by essential oil extracts from Cit. sinensis that may be used as a natural antimicrobial to treat various infections caused by pathogens of public health interest.