Multidrug-Resistant Escherichia coli Accumulated by Freshwater Bivalves: An Underestimated Risk for Public Health?

ABSTRACT

As bioindicators, freshwater bivalves are crucial for the assessment of the contamination impact on different levels of biological integration. Escherichia coli is used as a bioindicator of water fecal contamination, representing a critical global concern, especially with the rise of multidrug-resistant (MDR) strains. Phylogenetic diversity, pathotypic characterization, and antibiotic resistance profiles of E. coli isolated from freshwater bivalves (Anodonta anatina) were assessed. Samples were collected from the Tua River in Northern Portugal, from two different sites, Chelas and Barcel, representing different degrees of contamination. Antimicrobial susceptibility testing was performed by the disk diffusion method, and characterizations of the phylogenetic groups and pathotypes were assessed by PCR-multiplex and real-time PCR-multiplex, respectively. Results showed that 60% of isolates were characterized as MDR, including resistance to carbapenems, considered the last resort against multidrug-resistant bacteria. Within this study, it was also possible to verify the antimicrobial resistance (AMR) profile differences between the two sampling sites, with bivalve isolates from the Chelas site showing a higher percentage of antibiotic resistance. Among the E. coli isolates, the highest prevalence (55%) was observed in group B1, followed by group D or E (15%), group A (10%), and group E or Clade I (10%). None of the isolates were classified as diarrheagenic E. coli (DEC). This work highlights the potential transmission of antimicrobial-resistant bacteria through bivalves in the food chain. The 'One Health' approach is crucial for combating antimicrobial resistance, namely in edible freshwater species, emphasizing active surveillance to protect human, animal, and environmental health against the spread of antibiotic-resistant bacteria in aquatic environments.