Citrobacter freundii as a cause of disease in fish

Abstract

The paper describes an illness of one-year rainbow trout fry that was characterized by gastroenteritis and progressively high mortality, but which did not indicate a typical bacterial infection; and a clinical illness of cyprinids that indicated typical acute bacterial septicemia caused by Gram-negative bacteria. These diseases of rainbow trout and cyprinids were caused by the Gram-negative motile bacterium Citrobacter freundii. Cultures of Citrobacter freundii were isolated and identified on the basis of key phenotypic characters and with the aid of the Api 20 E system. Pathohistological examination confirmed inflammatory changes in the intestine of rainbow trout; and inflammatory and necrotic changes in the internal organs of cyprinids. We were able to reproduce the illness by means of artificial infection with a pure culture of Citrobacter freundii. This is the first published report confirming Citrobacter freundii as a cause of fish disease in Serbia.