Emergence of new and re-emergence of old infections continue to elude prospects of reducing morbidity and mortality caused by microbial infections. Trends of resistance to currently in use antimicrobials and antimalarials threaten to increase mortality caused by these infections. This study explores the potential of marine invertebrates as a source for new antimicrobials and antimalarials. The lactate dehydrogenase method was used to assay marine sponges for activity against
Plasmodium falciparum, while the disc diffusion method was used to assay the extracts for antibacterial and antifungal activity. Extracts of some marine sponges from the Zanzibar Island exhibited both antiplasmodial and antimicrobial activities. Among the 55 marine sponge extracts that were tested 23 (41.8%) inhibited
Plasmodium falciparum W2 strain by more than 50% at both 250 and 50 μg/ml concentrations. Moderate polar extracts were more active against
Plasmodium falciparum W2 strain than polar and non-polar extracts. None of the 12 extracts that were tested on
Plasmodium falciparum strain D6 exhibited inhibitory activity reaching 50%. Among 18 marine sponge extracts that were tested for antimicrobial activity 12 (66.7%) showed activity against one or more of the bacteria and fungi used ranging from weak to strong on an arbitrary criterion. The ethyl acetate extracts of
Agelas mauritania and
Oceanopia
sp. exhibited high activity against the fungi
Candida albicans
and
Cryptococcus neoformans
. The best antibacterial profile was exhibited by ethyl acetate extracts of
Aplysinopsis
sp.,
Halichondrida
sp. 1 and
Oceanopia sp. In conclusion, these results support the need for intensified efforts to search for active antimalarial and antimicrobial compounds from the Zanzibar marine sponges.
