Antibiotic Resistance in Ligurian Fauna

Antimicrobial resistance (AMR) represents one of the most critical global public health challenges of the twenty-first century, posing a serious threat to human, animal, and environmental health. The dissemination of resistant bacteria and resistance genes is increasingly recognized as a complex phenomenon driven by interactions among multiple ecological compartments, highlighting the need for integrated surveillance approaches within the One Health framework. This doctoral thesis investigates the role of wildlife and the environment as reservoirs and indicators of antimicrobial resistance in the Ligurian region (North-West Italy), an area characterized by high anthropogenic pressure and close interactions between urban, agricultural, terrestrial, and marine ecosystems. The first part of the thesis provides an extensive overview of the biological mechanisms underlying antimicrobial resistance, including enzymatic inactivation, target modification, efflux systems, and horizontal gene transfer. Particular attention is given to the environmental dimension of AMR and to the growing evidence supporting the role of natural ecosystems in the persistence and dissemination of resistant bacteria. The experimental section includes two complementary investigations. The first study focuses on the detection and characterization of Shiga toxin-producing Escherichia coli (STEC) isolated from wild ungulates in Liguria. Molecular analyses revealed the presence of virulence-associated genes, confirming the circulation of potentially pathogenic strains in wildlife populations and supporting their role as environmental sentinels at the human–animal–environment interface. The second study evaluates the occurrence of antimicrobial-resistant bacteria in marine bivalves (Mytilus galloprovincialis) collected along the Ligurian coastline within the “Mare in Rete” surveillance project. The results demonstrate the presence of E. coli strains exhibiting resistance to commonly used antimicrobial classes, particularly β-lactams and tetracyclines, with higher frequencies observed in coastal areas exposed to urban and wastewater-related pressures. Overall, the findings of this thesis highlight the relevance of wildlife and marine environments as early indicators of antimicrobial resistance circulation. The integration of terrestrial and marine monitoring provides valuable insights into environmental pathways of AMR dissemination and supports the implementation of coordinated One Health surveillance strategies at regional and national levels. Strengthening environmental monitoring systems is essential to improve risk assessment, guide preventive interventions, and mitigate the long-term impact of antimicrobial resistance on public health.