Ethanol extracts of Asparagopsis taxiformis collected from the Straits of Messina (Italy) were screened for antibacterial activity against pathogenic shellfish and fish bacteria previously isolated from local marine and brackish environments. Genetic labelling by DNA barcoding allowed us to identify the algal population as a biogeographical strain conspecific to A. taxiformis. The extract obtained in May showed the broadest antibacterial activity against all tested pathogenic bacteria, especially against Vibrio alginolyticus, Vibrio vulnificus and Aeromonas salmonicida subsp. salmonicida. Moderate activity was observed against Photobacterium damselae subsp. damselae and Photobacterium damselae subsp. piscicida, Salmonella sp., Vibrio cholerae, Vibrio harveyi and Vibrio parahaemolyticus. The absence of cytotoxic effects of active algal extracts was verified using trypan blue exclusion test on cells of digestive glands of Mytilus galloprovincialis. The results indicated that ethanol extracts of A. taxiformis could represent a source of antibacterial substances with potential use in aquaculture.
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