IN-VITRO EVALUATION OF EUCALYPTUS CITRIODORA LEAF ESSENTIAL OIL AND EXTRACTS ON SELECTED PATHOGENS IMPLICATED IN RESPIRATORY TRACT INFECTIONS

Public health challenge due to respiratory tract infections has necessitated vehement research for promising substances against the causative agents. The leaves of Eucalyptus citriodora (E. citriodora, Myrtaceae) are used in Nigeria as tea, infusion or steam inhalation by patients as an alternative medicine to clear the airway and relieve symptoms; however, no scientific evidence exists to support or debunk this claim. This study aimed to evaluate the in-vitro antimicrobial effect of E. citriodora leaf essential oil and crude extracts against selected pathogens implicated in respiratory tract infections. The fresh leaves of E. citriodora were collected, identified and subjected to exhaustive fractionated extraction. The leaf essential oil was obtained by hydrodistillation using Clevenger-type apparatus and characterized using GC-MS. Aqueous extracts were obtained by hot infusion and decoction and characterized using HPLC-UV-DAD. The susceptibility of test pathogens Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, Salmonella paratyphi ATCC 9150 Candida albicans ATCC 10231, Klebsiella pneumonia and Streptococcus pneumonia to the extracts were evaluated by agar well diffusion and agar dilution methods. Hydrodistillation gave colourless essential oil in yield of 3.5% (v/w). Monoterpenoids, citronellal (47%), isopulegol (8%), citronellol (8%), tetradecane-3-of (5%), citronellic acid (4%), p-methane-3,8-diol (4%), citronellylacetae (3%) and eucalyptol (1%) were the most abundant bioactive components. HPLC analysis of the infusion and decoction extracts revealed the presence of chlorogenic acid, caffeic acid, rutin, and ferulic acid. The essential oil and extracts produced good antimicrobial activities against the selected pathogens. The leaves of E. citriodora have bioprospecting potential in drug discovery for respiratory tract infections.