BIOACTIVITY TESTING OF SECONDARY METABOLITES FROM SELECTED SPONGES ALONG THE KENYAN COAST

Abstract

This thesis describes investigations on Axinella infundibuliformis, Haliclona oculata, Tethya citrina and Tethya sarai sponges collected along the Kenyan Coast. Through various chromatographic and spectroscopic techniques, three triterpene compounds were isolated and identified from A. infundibuliformis. These were 3β-hydroxylup-20(29)-ene (23), 3β-hydroxylup-20(29)-en-28-oic acid (24) and 3-oxolup-20(29) - en-28-oic acid (25). One sterol compound (β) beta- sitosterol (21) was isolated from H. oculata and from T. citrina, one compound pentyl heptacosanoate (22), a wax ester, was isolated.Hexane, dichloromethane and methanol crude extracts of A. infundibuliformis at 100 mg/ml showed the highest potential for antibacterial activity against methicilin resistant Staphylococcus aureus with inhibition zone diameters of 12.7 ± 0.1, 11 ± 2 and 6.7 ± 0.2 mm, respectively. The MIC values for dichloromethane and hexane extracts were then evaluated as at 6.25 and 3.12 mg/ml, respectively. All the crude extracts from H. oculata were inactive against all the bacteria and fungi strains tested. The antifungal tests indicated that crude extracts from A. infundibuliformis had low activity while all the other extracts were inactive was against Candida albicans with inhibition zone diameters of 5.7 ± 0.3, 6.0 and 6.7 ± 0.2 mm for methanol, dichloromethane and hexane extracts, respectively. In addition, the dichloromethane and hexane extracts conjured low activities against Microsporum gypseum (6.3 ± 0.1mm) and Cryptococcus neoformans (6.3 ± 0.1 mm), respectively.The isolated compounds β-sitosterol (21), pentyl heptacosanoate (22) and 3β-hydroxylup-20(29)-en-28-oic acid (24) were tested against the same bacteria strains at 10 mg/ml. They all showed activity against Pseudomonas aeruginosa but were inactive against the other strains except for β-sitosterol (21) which exhibited some activity against Salmonella typhi and Escherichia coli. The inhibition zone diameters against P. aeruginosa were; β-sitosterol (21); 24 ± 1 mm, pentyl heptacosanoate (22); 10.7 ± 0.1 mm and 3β-hydroxylup-20(29)-en-28-oic acid (24); 7.0 ± 0.1 mm, while gentamycin (Standard drug) had an inhibition zone diameter of 16.0 mm. The results indicate that whereas the crude extracts showed the potential to inhibit gram positive bacteria (methicilin resistant S. aureus), the isolated compounds showed the potential to inhibit gram negative bacteria (P. aeruginosa) which are known to be more difficult to inhibit (less susceptible to antibiotics) than gram positive bacteria.