In vitro antibacterial and antioxidant activities of methanolic and dichloromethanolic seed extracts of Kenyan Annona squamosal inn
Mwihia, Stephen Kiruthi
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Enterobacterial constitute a large family of Gram-negative bacteria which reside in the intestines of the animals and can be pathogenic. Penicillins and fluoroquinolones have been used as antibiotics to combat enterobacterial infections. Challenges in treatment of enterobacterial infections with conventional drugs have led the physicians to opt for phyto products and other alternative medicine for treatment of enterobacterial infections. Heavy bacterial load leads to oxidative stress. Annona squamosa (sugar apple) is used traditionally as an anti-infective and antioxidant. This study was carried out to determine the antibacterial and antioxidant activities of organic seed extracts of Annona squamosa. The fruits were collected from local farms at Mwea, Wang’uru Sub-county of Kirinyaga County and transported to Mount Kenya University laboratory. The seeds were air dried and then ground into a fine powder before being subjected to extraction with three different solvents: DCM, MeOH and DCM: MeOH (1:1). The extracts were screened for antibacterial activities against standard Gram negative microbial strains of Salmonella typhirium (ATCC 1408), Klebsiella pneumoniae (ATCC700603), Escherichia coli (ATCC 25922) and Shigella flexneri (ATCC 12022), that were procured from KEMRI. The results were obtained through the use of Agar-Disc Diffusion Method and minimal inhibitory concentration (MIC) of each extract noted. Discs impregnated with Ciprofloxacin were the standard while dimethyl sulfoxide (DMSO) was negative control. Sterile discs were dipped in different extracts concentrations for one minute and then placed on Luria Bertania agar plate inoculated with each bacterial species separately. Incubation of plates was done at 370C for 16 hours. The MIC of each extract with clear zones of inhibition was recorded in millimeters. The extracts were found to inhibit the test bacteria at varying degrees. The antibacterial data obtained was compared with that of the reference drug (Ciprofloxacin). The MeOH extract was the most efficacious in terms of inhibitory activities, exhibiting the MIC ranging from 15mg/ml to 31.17mg/ml. Methanol: DCM extract ranked second in terms of inhibitory activity with the MIC range of 16.4mg/ml to 56.57mg/ml, DCM showed the least inhibition activities with the MIC ranging from 47.50mg/ml to 61.83mg/ml. The extracts were found to possess antibacterial activities that were significantly lower compared from Ciprofloxacin, though in some concentrations they had the same zones of inhibition. The antioxidant activities of the extract were evaluated through scavenging effect of DPPH, H2O2 and the FRAP assay. The antioxidant data obtained was assayed against that of the standard (Ascorbic acid). The methanol extract was found to be the most potent extract with highest antioxidant activities. The qualitative photochemical screening indicated the presence of secondary metabolites associated with antioxidant and antibacterial activities. The present study therefore, recommends that organic seed extracts of Annona squamosa may undergo further research for development of phytomedicine with antibacterial and antioxidant properties.