Establishment and evaluation of BALB/c mice challenge model with lung pathogenic Escherichia coli O78 of forest musk deer origin

Abstract:

[Background] Lung pathogenic Escherichia coli (LPEC) belonging to extraintestinal pathogenic Escherichia coli was one of the important pathogens of zoonosis. [Objective] To establish a BALB/c mice challenge model of LPEC from forest musk deer for the study of pathogenicity of LPEC O78. [Methods] BALB/c mice were infected by LPEC O78 that was preserved in the laboratory, and the infection dose of model was determined by intraperitoneal inoculation to calculate LD50 (median lethal dose). The effect of mice model was evaluated based on monitoring the changes in bodyweight, biochemical indexes and bacterial colonization, and further evaluated by isolation of bacteria and histopathological examination. [Results] The LD50 of LPEC O78 in BALB/c mice was 3.6×108 CFU/mL. After infection, the challenge group showed that depressed, anorexic and sluggish symptom. Lung and liver enlarged, intestine hemorrhage was observed by necropsy after 3 h post-challenge. The bodyweight of mice decreased by 3.2 g within 24 h post-challenge, and then slowly increased. The biochemichel indexs of ALT, AST, TP, ALB, IP, Ca, Mg, TBIL, URIC, UREA, GLU, CHE and LDH in the challenge mice were higher than the mock mice (P<0.05), except the uric acid content (P>0.05). All organs had bacterial colonization, in which heart, spleen and kidney reached the highest at 24 h post-challenge whereas the time for highest colonization in liver, lung and intestine was 12 h post-challenge. Histopathological examination revealed different degree of inflammatory cell infiltration and necrosis. [Conclusion] This study successfully established the mice challenge model of LPEC O78 and laid a foundation for the future research of pathogenesis and pathophysiology of LPEC O78 from forest musk deer.