Blue Crab (Callinectes sapidus) Haemolymph as a Potential Reservoir of Mesophilic Shewanella Species

The blue crab (<i>Callinectes sapidus</i>) is an invasive alien species in the Mediterranean Sea, posing threats to biodiversity, fisheries, and aquaculture. Climate change has worsened these challenges, influencing the distribution of bacterial species, including <i>Shewanella</i> species, which are sensitive to changes in temperature and salinity. In this study, 300 blue crabs were sampled between June and October 2024 from the Sacca di Goro (Northern Adriatic Sea, Italy) to investigate the prevalence of <i>Shewanella</i> species in their haemolymph. The prevalence was found to be 7% (21/300), with species such as <i>S. mesophila</i>, <i>S. algae</i>, <i>S. cowelliana</i>, and <i>S. baltica</i> identified, particularly in the months of September and October. Molecular techniques, including MALDI-TOF MS and <i>rpoB</i> gene amplification, were used to identify isolates. Antibiotic susceptibility testing (AST) revealed a trend of resistance to beta-lactam antibiotics. A network analysis was also conducted to examine the global trends of <i>Shewanella</i> research in relation to humans, animals, and the marine environment. While proper cooking eliminates the risk to consumers, handling without personal protective equipment can increase exposure, particularly for vulnerable individuals such as those who are elderly or immunocompromised. Mild symptoms are observed in children. Further studies, particularly with a One Health approach, are crucial to better understand the transmission dynamics and evolving antibiotic resistance of <i>Shewanella</i> species.