Isolation and pathogenicity evaluation of Escherichia coli O157:H7 from common carp, Cyprinus carpio

Escherichia coli O157:H7 is the primary serotype of enterohaemorrhagic E. coli (EHEC), which can cause diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome. It is considered as a major health concern due to it being a zoonotic disease that is transmitted through food. In this study, a pathogenic bacterium was isolated from infected carp, which identified as E. coli O157:H7 named X21 through genetic sequencing, phylogenetic analysis, physiological and biochemical tests. In the experiment, crucian carp was used as a model to study the pathogenicity of the isolate, the pathological histological observations and cytokines expression of fish tissues were determined after bacterial challenge. The results showed that severe pathological damage observed in the liver, spleen, headkidney of fish infected with isolate X21. Besides, we found that accumulation of IgT+ B cells in the lamina propria of intestine, and up-regulation of SUCH-r, IL-1 & beta;, IL-10, IL-11, MyD88, and TNF-& alpha; gene in various tissues. After challenged, the survivability of crucian carp infected with isolate X21 stands at a mere 14.27%. To our knowledge, this is the first report that E. coli O157:H7 infected the freshwater fish C. carpio, which indicates that this bacterium is a potential threat to public health and freshwater fish aquaculture.

Automated summary

In this study, a pathogenic bacterium named X21, identified as Escherichia coli O157:H7, was isolated from infected carp through genetic sequencing, phylogenetic analysis, and physiological and biochemical tests. The pathogenicity of isolate X21 was studied using crucian carp as a model, and severe pathological damage in fish tissues was observed. The expression of IgT+ B cells and various cytokines in the tissues also showed significant changes. The survivability of crucian carp infected with isolate X21 was only 14.27%. This is the first report of E. coli O157:H7 infecting the freshwater fish C. carpio, indicating its potential threat to public health and freshwater fish aquaculture.