Antimicrobial and Antibiofilm Activity of Unionid Mussels from the North of Portugal

Abstract

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.

Clearance and persistence of Escherichia coli in the freshwater mussel Unio mancus

“…Organisms that detect environmental risks or changes in an ecosystem are considered sentinels 9 , 10 . In this sense, marine and freshwater bivalves should generally be considered sentinel species due to their filtration feeding system, which confers them with the capacity to concentrate organic (bacteria, phytoplankton, organic fragments) and inorganic particles from water 25 , 34 , 38 . For example, the E. coli removal capacity of oysters and hard-shelled clams 45 , common marine mussels 46 and freshwater bivalves such as D. polymorpha , Anodonta californiensis , Corbicula fluminea and Caruncilina texasensis 14 , 15 , 19 , 25 , 43 has been broadly assessed.…”

“…Unio mancus plays an important role in preserving and restoring water quality in impaired Mediterranean ecosystems 32 , 33 . However, its potential to act as a sentinel species has not yet been demonstrated 28 , 34 . The objectives of the present study were to determine the capacity of U. mancus to clear E. coli from water, to observe the viability of this bacterium in the soft tissue of the mussels, and to calculate the retention time under experimental conditions, in order to assess the mussel’s potential to act as a sentinel species in anthropogenically altered freshwater environments in the Mediterranean rivers.…”