First Report of Septicaemic Listeriosis in a Loggerhead Sea Turtle (Caretta caretta) Stranded along the Adriatic Coast: Strain Detection and Sequencing

Simple Summary Listeria is a ubiquitous bacterium responsible for outbreaks in humans and animals. Therefore, marine monitoring and detection of this bacterium are important for public health. This work presents the first case of Listeria monocytogenes in a stranded loggerhead sea turtle (Caretta caretta) with a severe septicaemic infection. Gross and microscopic lesions showed chronic inflammation of all tissues due to septicaemia. Furthermore, a microbiological investigation confirmed the presence of L. monocytogenes. Whole-genome sequencing (WGS) was performed on isolated colonies for deep characterization of the strain, and antibiotic resistance genes were identified from the sequence. Although there are increasing reports on the prevalence of Listeria monocytogenes in wild species, this is the first case of listeriosis in sea turtle. An adult female Caretta caretta was rescued after being stranded alive along the coast of the Abruzzo region (Italy) in summer 2021. The turtle died in 6 days due to respiratory failure. The necropsy showed widespread organ lesions, such as yellow foci of necrosis in many organs, gastrointestinal erosions, pericarditis, and granulomatous pneumonia. Microbiological and histological analyses were performed on several organs. Listeria monocytogenes was isolated from multiple organs, indicating a case of septicaemic listeriosis, and the genome was sequenced and characterized. All the colonies analysed belonged to the same strain serogroup IVb, ST388, and CC388.