Interferon is an important cytokine in the host defense against infection by viral and microbial pathogens. We determined quantitatively the antibacterial activity of the virus-resistant shrimp (Marsupenaeus japonicus) recombinant protein IntlP against three Gram-negative bacteria: Vibrio alginolyticus, Vibrio parahemolyticus and Vibrio vulnificus, using a turbidmetric assay with live bacteria and differential bacterial viable count after interaction with the protein. In conclusion, the antibacterial activity of recombinant shrimp protein IntlP against Vibrio sp is at least equal to the values against the Gram-positive Micrococus luteus and more active against the shrimp pathogens V. alginolyticus and V. parahemolyticus.