Establishment and Evaluation of Enteritis Model of Largemouth Bass by Aeromonas hydrophila Infection
[Objective]This study aimed to establish a stable bacterial enteritis model of largemouth bass(Micropterus salmoides)infected by Aeromonas hydrophila,and to determine the concentration and bacte-rial infection time which leading to enteritis.[Method]150 healthy largemouth bass were randomly di-vided into 5 groups:the control group and 4 experimental groups(the infection concentrations of bacteria were 1×108,1×107,1×106 and 1×105 CFU/mL,respectively).The fish was infected by intraperitoneal in-jection.The effect of modeling in each experimental group was evaluated by means of clinical symptom-atology,necropsy lesions and scores,histological changes and scores,intestinal tissue ultrastructural changes and inflammatory factor gene expression.[Result]The experimental groups fish showed slow swimming and decreased feeding after the infection,of which the death was appeared in the 1×108 CFU/mL group on the 2nd and 3rd day post-infection.After the autopsy,anal redness and swelling,protrusion,abdominal fin and abdominal skin bleeding,intestinal congestion and bleeding,intestinal fluid retention were showed in experiment groups.The gross pathological scores of each group were positively correlated with the bacterial infection concentration and negatively correlated with the post-infection time.Histologi-cal observation showed that the intestinal lamina propria was hyperemic,edematous,thickened,accom-panied by inflammatory cell infiltration,mucosal epithelial damage and shedding,cell degeneration,ne-crosis,hyperplasia,and the number of goblet cells significantly increased.The histological score in-creased with the increase of bacterial concentration,which showed a trend of first increasing and then de-creasing with the post-infection day,with the highest histological score on the 5th post-infection day.The ultra-structure morphological disorders in intestinal tissue were observed,which were positively cor-related with the infection concentration.The microvilli were observed to be damaged and shed to varying degrees.The arrangement of epithelial cells was disordered,the mitochondria were edema,the structure was incomplete,and vacuoles appeared.The endoplasmic reticulum expanded,the organelles in some cells'cytoplasm dissolved or even disappeared,and the number of goblet cells increased.The change in the expression of inflammatory factors was related to the concentration of bacteria.Ultrastructural changes of intestinal tissue showed that intestinal microvilli in the challenge group were damaged and shed,their morphology was disordered,epithelial cell arrangement was disordered,mitochondrial edema and vacu-oles appeared,organelles dissolved or even disappeared in some cell envelope and the number of goblet cells increased.The changes in the expression of inflammatory factors in each experimental group were re-lated to bacterial concentration.The expression of IL-15,IL-8,TNF-α and IL-1β increased with the in-crease of bacterial concentration,and showed a trend of first increasing and then decreasing with post-infection day.The expression of IL-10,IL-11 and TGF-β2 was negatively correlated with infection con-centration,and the gene expression of IL-10 and IL-11 was significantly lower than that of the control group,while the gene expression of TGF-β2 had no significant difference.[Conclusion]There was no death during the whole experiment in the 1×107 CFU/mL challenge group,the pathological damage was observed in the intestinal.Therefore,in order to establish a model of intestinal injury close to clinical conditions,a bacterial solution with a challenge dose of 200 μL 1×107 CFU/mL was selected as the infec-tion concentration to the intestinal pathological injury model.
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