ANTIMICROBIAL ACTIVITY AND SURFACE BACTERIAL FILM IN MARINE SPONGES

The antimicrobial activity of three sponge species was tested against marine benthic bacteria and the presence of epibiotic bacteria on their surfaces was investigated. The aim of the present study was to determine whether there is a correlation between antimicrobial activities and the presence of a bacterial film. Seven benthic bacterial strains were isolated from the vicinity of the sponges and used as assay organisms. Gram-positive and Gram-negative bacteria were equally affected by all the sponge extracts. The encrusting sponge Crambe crambe featured the strongest antimicrobial activity in the assays and no bacteria were found on its surface. The other two sponges, Ircinia fasciculata and Spongia officinalis, featured lower antimicrobial activity than C crambe and the number of bacteria found on their surfaces was of the same order of magnitude as that found on immersed glass slides used as controls. It was concluded that antimicrobial activities detected in laboratory assays were effective as mechanisms to combat microfouling in only some cases, and other possible interpretations are considered.