Antibacterial Activity of Marine Sponge Extracts against Fish Pathogenic Bacteria

Secondary metabolites of the marine sponges Acanthella elongata, Axinella donnani, Callyspongia diffusa, Callyspongia subarmigera, and Echinodictyum gorgonoides were collected from fishing nets and their in vitro antibacterial properties against eight virulent marine fish pathogens were studied at incubation temperatures of 20°C and 30°C. Crude methanol extracts of the tested sponges showed species-specific antibacterial activity. The most active species was A. elongata which inhibited 100% and 87.5% of the tested bacterial isolates at 20°C and 30°C, respectively. Callyspongia subarmigera was the least active as it inhibited only 62.5% and 50% of the tested bacteria at those temperatures. Results suggest that fractionation and purification of the crude methanol extract of A. elongata has potential in the development of novel antibiotic substances for managing common bacterial diseases in aquaculture. Introduction The evolving resistance of microorganisms to existing antibiotics has made necessary a search for new antibiotics for human as well as aquacultural purposes. In the aquatic environment, competition for space and nutrients leads to evolution of antimicrobial defense strategies. This, along with possibly adverse effects on the ecosystem and human health problems, has resulted in restrictions on the use of commercial antibiotics and chemicals in the aquatic environment (Serrano, 2005). Bacteria that are resistant to antibiotics must be tackled with more effective and safer antibiotics. Such substances include natural products derived from marine organisms (Selvin and Lipton, 2004). Sessile, soft-bodied marine invertebrates such as sponges lack obvious physical defenses and biosynthesize bioactive non-primary or secondary metabolites to protect themselves and maintain homeostasis (Attaway and Zaborsky, 1993). Sponges have antibacterial, antifungal, antiviral, antihelminthic, anticoagulant, antitumour, cytotoxic, antidiabetic, antiinflammatory, antimalarial, antiplatelet, antiprotozoal, antileukemic, anti* Corresponding author. E-mail: [email protected]