The aim of this study is to identify the cause of death of a South China tiger cub at the Meihuashan breeding institute of Fujian Province.Pathogenic bacteria were isolated and cultured from liver,spleen,lung and other tissue samples of the dead South China tiger aseptically.The iso-lated bacteria were identified through morphological observation,biochemical characterization,sequence analysis of housekeeping gene gyrB,virulence gene detection,animal pathogenicity test and drug sensitivity test.A pathogenic Aeromonas hydrophila strain,designated FJ/Tiger-201809 was successfully isolated from the trachea of dead South China tiger.The nucleotide sequence ho-mology between the isolate and 11 strains of Aeromonas gyrB ranged from 91.2％to 99.1％,with the highest homology of 99.1％observed with Aeromonas hydrophila(AF208251.1).Genetic evo-lution analysis showed that the isolated strain FJ/Tiger-201809 was in the same evolutionary branch as other reference strains of Aeromonas hydrophila and was closely related.The pathoge-nicity test in mice showed artificial infection of mice with the strain resulted in varying degrees of lesions in several organs of the mice,and the median lethal dose(LD50)was 1 × 107.8 CFU/mL.Virulence gene test results showed that the isolate FJ/Tiger-201809 carried two virulence genes,aer and act.The results of drug sensitivity test showed that FJ/Tiger-201809 was highly sensitive to enrofloxacin and ampicillin among 18 commonly used antibiotics,relatively sensitive to penicil-lin G and doxycycline,and resistant to the other 14 antibiotics.In conclusion,this study isolated and identified a strain of Aeromonas hydrophila from a dead South China tiger with multiple drug resistance and strong pathogenicity,which provided an important reference for the prevention and control of bacterial diseases in South China tiger.

The aim of this study is to identify the cause of death of a South China tiger cub at the Meihuashan breeding institute of Fujian Province.Pathogenic bacteria were isolated and cultured from liver,spleen,lung and other tissue samples of the dead South China tiger aseptically.The iso-lated bacteria were identified through morphological observation,biochemical characterization,sequence analysis of housekeeping gene gyrB,virulence gene detection,animal pathogenicity test and drug sensitivity test.A pathogenic Aeromonas hydrophila strain,designated FJ/Tiger-201809 was successfully isolated from the trachea of dead South China tiger.The nucleotide sequence ho-mology between the isolate and 11 strains of Aeromonas gyrB ranged from 91.2％to 99.1％,with the highest homology of 99.1％observed with Aeromonas hydrophila(AF208251.1).Genetic evo-lution analysis showed that the isolated strain FJ/Tiger-201809 was in the same evolutionary branch as other reference strains of Aeromonas hydrophila and was closely related.The pathoge-nicity test in mice showed artificial infection of mice with the strain resulted in varying degrees of lesions in several organs of the mice,and the median lethal dose(LD50)was 1 × 107.8 CFU/mL.Virulence gene test results showed that the isolate FJ/Tiger-201809 carried two virulence genes,aer and act.The results of drug sensitivity test showed that FJ/Tiger-201809 was highly sensitive to enrofloxacin and ampicillin among 18 commonly used antibiotics,relatively sensitive to penicil-lin G and doxycycline,and resistant to the other 14 antibiotics.In conclusion,this study isolated and identified a strain of Aeromonas hydrophila from a dead South China tiger with multiple drug resistance and strong pathogenicity,which provided an important reference for the prevention and control of bacterial diseases in South China tiger.

The outbreak of coronavirus disease (COVID-19) caused by SARS-CoV-2 virus continually lead to worldwide human infections and deaths. Currently, there is no specific viral protein-targeted therapeutics. Viral nucleocapsid protein is a potential antiviral drug target, serving multiple critical functions during the viral life cycle. However, the structural information of SARS-CoV-2 nucleocapsid protein remains unclear. Herein, we have determined the 2.7 Å crystal structure of the N-terminal RNA binding domain of SARS-CoV-2 nucleocapsid protein. Although the overall structure is similar as other reported coronavirus nucleocapsid protein N-terminal domain, the surface electrostatic potential characteristics between them are distinct. Further comparison with mild virus type HCoV-OC43 equivalent domain demonstrates a unique potential RNA binding pocket alongside the -sheet core. Complemented by binding studies, our data provide several atomic resolution features of SARS-CoV-2 nucleocapsid protein N-terminal domain, guiding the design of novel antiviral agents specific targeting to SARS-CoV-2.

BACKGROUND:Toxic effects of excessive thyroid hormone on myocardium can not be ignored with the increased incidence of hyperthyroidism. As a quantitative marker of heart failure, brain natriuretic peptide has a good application prospect to estimate the changes of cardiac function and myocardial damage in hyperthyroid cardiomyopathy. OBJECTIVE:To explore the correlation of brain natriuretic peptide and cardiac function of rabbits with hyperthyroid cardiomyopathy exhibiting different left ventricular geometries. METHODS:Twenty New Zealand purebred rabbits were used in this study. Hyperthyroidism model was established by intraperitoneal injection of levothyroxine (45 μg/kg) for 4 weeks. The success of establishing model is defined upon the appearance of irritation, decreased body weight and increased appetite. Totaly 18 rats were successfuly established. The left ventricular data of hyperthyroidism rabbits were measured by conventional echocardiography. According to the classification of Ganauet al, the 18 hyperthyroidism rabbits were divided into two groups: concentric hypertrophy (n=7) and eccentric hypertrophy (n=11). In addition, ten rats, receiving intraperitoneal injection of 5 mL saline per day, were taken as the control group. RESULTS AND CONCLUSION: Plasma brain natriuretic peptide level of rabbits in the concentric hypertrophy and eccentric hypertrophy groups was obviously higher than that of the control group (alP < 0.01), and the level in the eccentric hypertrophy group was obviously higher than in the concentric hypertrophy group (P< 0.01). Compared with the control group, the average peak diastolic velocity of mitral ring was significantly lower in the concentric hypertrophy and eccentric hypertrophy groups (alP< 0.01), the average peak systolic velocity of mitral ring was also lower in the eccentric hypertrophy group (P < 0.01). The peak systolic and diastolic velocity had a negative correlation with brain natriuretic peptide (alP < 0.01). Experimental findings indicate that brain natriuretic peptide is a sensitive indicator to reflect the cardiac function and myocardial damage in rabbits with hyperthyroid cardiomyopathy, exhibiting different left ventricular geomeies.