D-amino acid peptides as antimicrobial agents against vibrio-associated diseases in aquaculture

Vibriosis is one of the most usual infection diseases in bivalve mollusks, particularly affecting seeds and larvae, which are more susceptible than adults to these bacterial infections. The devastating effect of vibriosis in shellfish hatcheries is aggravated by the increasing resistance of many Vibrio species to traditional antibiotics, highlighting the need to find new antimicrobial agents. Antimicrobial peptides (AMPs) are a promising alternative, however, their low stability can be a handicap for their practical application. In this study, the 3D structure and the stability of a synthetic all-D-amino acid peptide (D-Caerin) to proteases and extreme pH conditions have been analyzed and compared with its corresponding natural L-enantiomer peptide, Caerin 1.1. Moreover, the antimicrobial activity of D-Caerin has been tested in vitro against the control bacteria Micrococcus luteus CECT 245; and four Vibrio species: Vibrio aestuarianus CECT 625 T, Vibrio anguillarum CECT 522 T, Vibrio harveyi CECT 525 T and Vibrio tapetis CECT 4600 T, which are among the most representative causative agents of vibriosis in aquaculture. Our results demonstrate that D-Caerin contains two left-handed alpha helices, and is more stable and effective against the bacterial species tested than its corresponding natural L- counterpart. The bioactivity of D-Caerin has also been tested in vivo, in clam seeds infected with a mixed inoculum of these vibrio species. These preliminary assays show that D-Caerin-treated specimens exhibit higher survival rates after infection, demonstrating the superior stability of D-Caerin and its effectiveness against vibriosis-causative agents.