Freshwater mussels are among the most endangered groups of fauna anywhere in world. The indiscriminate use
of antibiotics has led to the emergence of resistant strains. These antibiotic-resistant bacteria play a key role in
increasing the risk allied with the use of surface water and in spread of resistance genes. Two endangered
freshwater mussel species, Margaritifera margaritifera and Potomida littoralis, were sampled at 4 sampling sites
along a 50 km stretch of River Tua. Water samples were taken at same sites. Of the total of 135 isolates, 64.44%
(39.26% from water and 25.19% from mussels) were coliform bacteria. Site T1, with the lowest concentration of
coliform bacteria, and site T2 were the only ones where M. margaritifera was found. No E. coli isolates were found
in this species and the pattern between water and mussels was similar. P. littoralis, which was present at T3/T4
sites, is the one that faces the highest concentration of bacterial toxins, which are found in treated wastewater
effluents and around population centers. Sites T3/T4 have the isolates (water and mussels) with the highest
resistance pattern, mainly to β-lactams. Water and P. littoralis isolates (T3/T4) showed resistance to penicillins
and their combination with clavulanic acid, and to cephalosporins, precisely to a fourth generation of cephalosporin
antibiotics. The analysis provides important information on the risk to water systems, as well as the need
to investigate possible management measures. It is suggested that future studies on the health status of freshwater
bivalves should incorporate measures to indicate bacteriological water quality.
This work was supported by the Portuguese Foundation for Science and Technology (FCT) and the Operational Competitiveness Programme (COMPETE), under projects UIDB/04033/2020 and UIDP/04033/2020 (CITAB-Inov4Agro-UTAD). This research was also funded by the Conselleira de Educación, Universidade e Formación Profesional, Xunta de Galicia, Spain, under project R815 131H 64502 (Xana Álvarez). Funding for open access charge was from the Universidade de Vigo/CISUG.
