Biocide development for hard surfaces using extracts and compounds from Callistemon citrinus

Abstract

The global is now focusing on the use of herbal products and among them are herbal disinfectants. Plants contain a variety of secondary metabolites which include phenolic compounds, tannins, terpenoids, alkaloids and flavonoids. C. citrinus is a plant native to Australia which have been found to have antimicrobial properties. Herbal products can be environmentally safe as they are biodegradable and prevent environmental contamination. The aims of the study where to use the extracts from C. citrinus leaves to make a disinfectant to be used for cleaning hard surfaces. The test microorganisms to determine the antimicrobial activity of the C. citrinus leaf extract were S. aureus, E. coli and C. albicans. The leaves were dried and ground into a coarse powder which was used for the extraction process. Both total extraction and serial exhaustive extraction were used to obtain extracts from the leaves. The antimicrobial activities of the extracts were determined using the microbroth dilution method. The MTT assay was used to determine the viable cells after incubation of the test microbes and the extracts. The MIC was determined for the most potent extracts where total inhibition was observed. The hexane, DCM, ethyl acetate and acetone extracts of C. citrinus were effective against S. aureus. The ethanol extract had the highest inhibitory activity against C. albicans and E. coli was resistant to all the extracts tested against it. The MIC for the hexane extract was 50 μg/ml and for the DCM extract it was 25 μg/ml against S. aureus. The ethyl acetate extract had an MIC of 100 μg/ml against S. aureus. The DCM extract was used to formulate the disinfectant and formulation 1 was prepared using sulphonic acid and sodium hydroxide as the base. Formulation 2 was prepared using glycerine as the base. The agar disk diffusion method was used to test the effectiveness of the disinfectants formulated. Formulation 1 and 2 activity was tested against S. aureus, C. albicans and E. coli. S. aureus and C. albicans were susceptible to both formulations, the base for formulation 1 had antimicrobial activity as ZOI were observed around the disks containing the base as the negative control. E. coli was resistant to both formulations.