First Report, Pathology and Antimicrobial Profile of an Infection with Citrobacter youngae in a Species of Wild-caught Carp in Türkiye

Citrobacter spp. are classified as Gram-negative, non-spore forming, rod-shaped, facultative anaerobic bacteria that have been identified in a variety of environmental and biological specimens. These include soil, sewage, mud, water, food, and the intestines of humans and animals. It has been determined that Citrobacter spp. accounts for 3–6% of all isolates from the Enterobacteriaceae family that have been implicated in nosocomial infections. The aquacultural industry produces fish as a highly nutritious foodstuff. This product is marketed and consumed worldwide in a variety of forms and culinary preparations, and constitutes a significant part of the human diet. Nevertheless, fish is also highly susceptible to deterioration and contamination by microorganisms at every stage of the food chain. The extant literature contains an insufficient amount of information regarding Citrobacter youngae and its implications for human and animal health. The present study detected C. youngae in four different carp species, which were obtained from natural sources by culture and MALDI-TOF method. Furthermore, the study determined the pathological findings and antibiotic sensitivity of the pathogen. A total of 48 fish samples were analyzed, and C. youngae was isolated from 26 samples, including liver, kidney, gill and muscle tissues. The fish samples exhibited symptoms such as abdominal bloating, exophthalmos, petechial haemorrhages on the skin and haemorrhages at the bases of the fins, around the anus and mouth, especially in the upper and lower jaws. C. youngae demonstrated susceptibility to ampicillin, ampicillin-sulbactam, amoxicillin-clavulanate, piperacillin-tazobactam, cefepime, ceftriaxone, imipenem, ciprofloxacin, levofloxacin, moxifloxacin, gentamicin, amikacin, and tobramycin. However, resistance was observed for trimethoprim-sulfamethoxazole, cefotaxime, ceftazidime, ertapenem, and meropenem. Consequently, C. youngae was identified in wild-caught carp species, signifying the inaugural documentation of this bacterium with regard to both clinical observations and antibiotic profiles. Rigorous monitoring of this bacterium is imperative in the context of both aquaculture and public health.