Isolation,Identification And Antibiotic Sensitivity Analysis Of Citrobacter Braakii From Procambarus Clarkii

The Procambarus clarkii is commonly known as crayfish that was transmitted from Japan to Nanjing in 1929.The former has a strong adaptability.It is mainly distributed in the Yangtze River basin in China,including Jiangsu,Zhejiang,Hubei,Hunan,Anhui,Shandong and other more than 10 provinces and regions.It has been reported that in August 2017,the country's crayfish aquaculture output was 950,000 tons,with an area of more than 600,000 hm².It is expected that in 2018,the area under shrimp cultivation will exceed 660,000 hm²,with production reaching 1 million tons.The amount of Procambarus clarkii is increasing year by year,but has been suffering from disease.The diseases that have been reported so far include crab spiral body,white spot syndrome virus,Aeromonas hydrophila,Vibrio parahaemolyticus,Aeromonas veronii,and so on.Citrobacter is commonly found in Gram-negative bacteria in soil,water and other natural environments.It is a normal flora in the intestinal tract of animals and humans.When the body's resistance is reduced,this genus bacterium can cause the infection of humans,terrestrial animals and certain aquatic animals.C.braakii is a conditional pathogen commonly found in human feces or animals.In 2017,a large number of deaths occurred in the Procambarus clarkii farmed in an aquaculture farm in Anhui Province.The laboratory used the ice box to bring back more than 10 shrimps from the farm for disease diagnosis.Through the dissection of the diseased shrimp,it was found that there was a lot of ascites under the thoracodorsalis,and the edema of the hepatopancreas was darkened.A dominant strain AX1707 was isolated and purified from the hepatopancreas of diseased shrimp.Physiological and biochemical identification results showed a negative oxidase,Gram-negative and Citrobacter burgdorferi.Through the 16S rRNA gene amplification,sequencing and phylogenetic tree analysis of AX1707 strain,the results showed that AX1707 and Citrobacter brucei?GenBank serial number:CP022049.1?gathered one.Artificial infection experiment results showed that the bacterium had a strong pathogenicity,and the LD₅₀ was 4×10⁶ CFU/ml.The antimicrobial susceptibility testing showed that AX1707 was sensitive to enrofloxacin,ofloxacin,TMP/SMZ,gentamicin and doxycycline,and was intermediate to tetracycline and fradiomycin,and resistance to erythromycin and ampicillin.After using TMP/SMZ in the farm,the effect was significant.This study reports for the first time that Citrobacter braakii caused the onset of Procambarus clarkii.The experimental results will provide some reference for the prevention and cure of bacteriosis of Procambarus clarkii.