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 <i>Citrobacter</i> 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 <i>Citrobacter</i> spp. in a loggerhead sea turtle (<i>Caretta caretta</i>) 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-β-lactamase (ESBL) <i>bla_CTX-M</i>, <i>bla_TEM</i>, <i>bla_SHV</i>, <i>bla_PER</i>, and metallo-β-lactamase (MBL) <i>bla_IMP</i>, <i>bla_OXA-48</i>, <i>bla_VIM</i>, <i>bla_NDM</i>, <i>bla_GES</i> genes. Biofilm production ability was also evaluated. Fifteen <i>Citrobacter</i> 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 <i>bla_SHV</i> and <i>bla_PER</i> genes (60%), while the most frequently detected MBL gene was <i>bla_NDM</i> (46.7%), followed by <i>bla_GES</i> (40%). Most isolates were classified as weak biofilm producers (80%). The findings of this study demonstrate the presence of <i>Citrobacter</i> 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.