Screening for antibacterial and antiviral activities in three bivalve and two gastropod marine molluscs

The aim of this study was to identify the presence of antimicrobial activities in the hemolymph of commercially important mollusc species. Acidic extracts were prepared from whole Cerastoderma edule (Cardiidae), Ruditapes philippinarum (Veneridae), Ostrea edulis (Ostreidae), Crepidula fornicata (Calyptraeidae) and Buccinum undatum (Buccinidae) and fractionated by Solid Phase Extraction. Fractions were first assayed for antibacterial activity against two indicator strains by an antagonism well diffusion method. Minimal Inhibitory Concentrations (MICs) were then determined against a panel of target bacteria including three Gram-positive and seven Gram-negative bacteria, some of which are aquaculture-pathogenic marine strains. In parallel, antiviral activities were assayed in vitro against Herpes simplex virus type 1 and Vero cells by cell viability. The broadest antibacterial activity was found in fractions from C. edule, but the highest activity was found in O. edulis (gills + mantle). At the antiviral level, the most active fraction was also attributed to C. edule acidic extract. Furthermore, SPE-fractions from other molluscs (40% SPE-fraction from O. edulis (gills + mantle), and 80% SPE-fractions from B. undatum, C. edule and R. philippinarum extracts) displayed lower EC50 values than the 40% SPE from C. edule but at in vitro concentrations causing more cytotoxicity. These promising results have led us to consider purification of the active compound(s) which may be related to mollusc defense mechanisms.