Potential zoonotic agents in sea turtles: Chlamydia species and Listeria monocytogenes

BACKGROUND: Sea turtles are well recognized sentinels of marine environment as well as carrier of pathogens and contaminants. Chlamydial species have been described in reptiles, but scarce data regarding sea turtles are available in literature (Pace et al., 2022). Hitherto, only one case of listeriosis has been described in marine reptiles (Di Renzo et al., 2022). This study reports the detection of Chlamydia species and Listeria monocytogenes in loggerhead sea turtles (Caretta caretta), suggesting the role of these animals as carriers of potential zoonotic agents. METHODS: In 2022, a total of 11 sea turtles found stranded along Emilia-Romagna coast, Northwestern Adriatic Sea, were subjected to post mortem investigation. Cloacal swabs were collected from 10 of the investigated animals and screened for Chlamydiaceae family by qPCR targeting 23S rRNA gene, followed by confirmation via 16S rRNA fragment sequencing. For positive samples, Chlamydia species identification was performed by species-specific qPCR for C. abortus, C. pneumoniae, C. pecorum, C. psittaci. One subject showed internal organs disseminated with multiple nodular lesions that were sampled for histopathology analyses, alongside microbiological examination. The cultured isolates were identified by MALDI-TOF (MALDI Biotyper; Bruker Daltonics Inc). RESULTS: In six out of 10 cloacal swabs Chlamydiaceae DNA was demonstrated by qPCR and confirmed by sequencing of 16S rRNA, but species identification was not achieved. In the turtle with nodular lesions, histopathology revealed the presence of granulomas: the Ziehl-Neelsen stain was negative for acid-fast organisms. L. monocytogenes was isolated from heart and liver and listeriosis was diagnosed. CONCLUSIONS: The results highlight how sea turtles can be carriers, symptomatic or not, of pathogens relevant for public health. Given the zoonotic potential of these microorganisms, particular precautions are recommended especially for professionals handling these animals. KEY MESSAGES: • Sea turtles can play an active role as carriers of possibly pathogenetic microorganisms. • Further studies of molecular identification of Chlamydia spp. from sea turtles are needed in atypical strains.