The populations of freshwater mussels belonging to the family Unionidae have been facing drastic changes in
terms of diversity and numbers caused by constant aggressions on their natural habitat. Nevertheless, bivalves are capable of
developing strategies of defense to overcome potential aggressors. The present work aimed to assess the potential antibacterial
capacity of different species of unionid mussels from the north of Portugal. For this purpose, circulating cells (hemocytes), fluids,
and mucus were obtained by nonlethal methods from the species Anodonta anatina (Linnaeus), Anodonta cygnea (Linnaeus),
Potomida littoralis (Cuvier), and Unio delphinus (Spengler), and tested against bacterial reference strains and multidrug-resistant
isolates. The cellular fraction of A. anatina, A. cygnea, and P. littoralis showed antibacterial activity, detected by the agar disc
diffusion method, against Bacillus subtilis ATCC 6683, Pseudomonas aeruginosa ATCC 27853 and Acinetobacter baumannii
ATCC 19606. Circulating cells from P. littoralis and A. anatina also inhibited Listeria monocytogenes ATCC 19111 and A. cygnea
has also inhibited a multidrug-resistant isolate of Pseudomonas putida. The plasma of all mentioned freshwater mussels, used
directly or diluted, showed great ability to hamper or inhibit the biofilm formation of Staphylococcus aureus ATCC 25923, P.
aeruginosa ATCC 27853, and Escherichia coli ATCC 25922. Anodonta cygnea hampered the biofilm formation by Enterococcus
faecalis ATCC 29212 as well. Overall, these results showed that not only cells play a relevant role in the immune system of these
species but also the plasma, which likely contains antibiofilm substances. Anodonta cygnea stood out by presenting the best
antibacterial inhibition potential.
This work was supported by the Portuguese Foundation for Science and Technology (FCT) with a research grant to M. H. (SFRH/BD/76265/2011). This article was also supported by the project INNOVMAR-Innovation and Sustainability in the Management and Exploitation of Marine Resources (NORTE-01-0145-FEDER-000035, within Research Line NOVELMAR), by North Portugal Regional Operational Programme(
NORTE2020), under the PORTUGAL2020 Partnership Agreement, and through the European Regional Development
Fund (ERDF).
