Occurrence of Citrobacter spp.-Associated and Non-Associated Lesions in a Stranded Loggerhead Sea Turtle (Caretta caretta) from Italy

The skin of turtles, particularly aquatic species, can harbor a diverse range of bacteria, including Citrobacter species, which are recognized as causative agents of Septicemic Cutaneous Ulcerative Disease. Consequently, turtles may act as reservoirs of pathogenic and multidrug-resistant bacteria, posing a potential public health concern. This case-based study investigated the presence of Citrobacter spp. in a loggerhead sea turtle (Caretta caretta) housed at the Livorno Aquarium, Italy. Nine swabs were collected from skin lesions (plastron, carapace, nuchal mass), the oral cavity, and the cloaca. The isolated strains were identified by MALDI-TOF MS and tested for their susceptibility to 12 antimicrobials, belonging to eight antimicrobial classes, by the disc diffusion method. Isolates were investigated genotypically for extended-spectrum-beta-lactamase (ESBL) blaCTX-M, blaTEM, blaSHV, blaPER, and metallo-beta-lactamase (MBL) blaIMP, blaOXA-48, blaVIM, blaNDM, blaGES genes. Biofilm production ability was also evaluated. Fifteen Citrobacter spp. strains were recovered from the analyzed samples. Complete resistance was recorded for ampicillin, followed by high levels of resistance to imipenem, tetracycline and piperacillin-tazobactam. Worryingly, 86.7% were classified as multidrug-resistant. The most common ESBL-genotype combination was blaSHV and blaPER genes (60%), while the most frequently detected MBL gene was blaNDM (46.7%), followed by blaGES (40%). Most isolates were classified as weak biofilm producers (80%). The findings of this study demonstrate the presence of Citrobacter spp., an opportunistic pathogen, with a notable prevalence of multidrug-resistant strains carrying beta-lactamase-encoding genes, in a loggerhead sea turtle in Italy, across both lesioned and healthy anatomical sites.