Synergistic activity of an antibacterial peptide from Atlantic cod (Gadus morhua L.) with other antibacterial agents

Disease management in aquaculture involves the use of antibacterial agents against infections. However, there is a growing concern over the resistance of bacteria to different antibiotics. Therefore, it is crucial to reduce the use of conventional antibiotics and to find alternative novel antibacterial agents to manage diseases and antibiotic-resistant bacteria. In this study, we have observed the in vitro antibacterial activity and the capacity of synthetic cod piscidin (SCP) from Atlantic cod to permeate the bacterial membrane. Moreover, we have investigated in vitro the synergistic activity of SCP with conventional antibiotics, including oxolinic acid (OXA), oxytetracycline hydrochloride (OTC), and sulfadiazine-trimethoprim combination (ST). Five test bacteria including Micrococcus lysodeikticus, Planococcus citreus, Yersinia ruckeri, Vibrio anguillarum, and Aeromonas salmonicida were used for the synergistic study. The antibacterial activity data revealed a moderate synergism in the following cases: OXA with SCP against V. anguillarum; OTC with SCP against V. anguillarum and A. salmonicida; and ST with SCP against M. lysodeikticus, A. salmonicida and Y. ruckeri. In contrast, no synergism was seen between all the three test antibiotics and SCP against P. citreus. Our results imply that the application of SCP along with the antibiotics inhibits the growth of some fish pathogens (Y. ruckeri, V. anguillarum, and A. salmonicida) and could considerably reduce the usage of conventional antibiotics. Therefore, SCP is a potential alternative agent in disease control in commercial cod farming.