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

## TL;DR

Blue crabs in Italy can carry antibiotic-resistant Shewanella bacteria, posing a health risk if not cooked properly.

## Contribution

Identified Shewanella species in blue crab haemolymph and their antibiotic resistance patterns in a marine environment.

## Key findings

- Shewanella species were found in 7% of blue crabs, particularly in September and October.
- Some isolates showed resistance to beta-lactam antibiotics.
- Proper cooking is recommended to prevent infection risks, especially for vulnerable individuals.

## Abstract

This study was conducted to understand whether blue crabs living in the Sacca di Goro lagoon (northeast Italy) could be carriers of bacteria that may pose a risk to people or the environment. Some of these crabs had a bacterium called Shewanella in their haemolymph, especially during the warmer months of September and October. These bacteria are usually found in the sea but can occasionally cause infections in humans. Some were also resistant to certain antibiotics, which makes treatment more difficult in the event of an infection. Our findings suggest that vulnerable people, such as those with weakened immune systems, should be cautious when handling raw crabs and that crabs should always be properly cooked before consumption. These results underscore the importance of continued research into bacterial transmission dynamics at the human–animal–environment interface, with implications for both public and marine health.

The blue crab (Callinectes sapidus) 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 Shewanella 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 Shewanella species in their haemolymph. The prevalence was found to be 7% (21/300), with species such as S. mesophila, S. algae, S. cowelliana, and S. baltica identified, particularly in the months of September and October. Molecular techniques, including MALDI-TOF MS and rpoB 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 Shewanella 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 Shewanella species.