A case study of Escherichia coli infection in super severe immunodeficient SPF mice

Nie Yongsheng; Gao Qiuwei; Zhou Shuo; Wang Wei

Abstract：The experiment was designed to investigate the cause of death in super severe immunodeficient SPF mice.300 super severe immunodeficient SPF mice(5～6 weeks old,female,weight 20～25 g)were purchased by the laboratory.Upon arrival,it was discovered that three mice had died,and subsequently,five more died during the follow-up quarantine period.The gross pathological anatomy of five mice without autolysis was performed,the relevant lesions were observed and photographed,and the disease materials were directly smeographed with Gram staining for microscopic examination.Meanwhile,the disease materials were collected and smeographed with lines in ordinary sterile AGAR dishes and McConkey dishes for 48 h after culture,colony morphology was observed,and colonies were selected for microscopic examination after Gram staining.The bacterial culture products from the disease samples were identified by biochemical tests and mass spectrometers.After obtaining the identification result,a challenge test was carried out to verify the pathogenicity of the standard strain.The results showed that there was a large amount of fibrous exudation in the thoracic cavity,the heart and lungs were covered by jelly,and the liver was covered by exudation,which was consistent with the phenomenon of'wrapped around the heart and liver'described by veterinary pathology.A small number of inflammatory cells and a large number of Gram-negative brevibacterium were detected by direct smear microscopy,and the bacteria cultured was identified as single Escherichia coli.In the challenge test,some mice given bacterial solution showed symptoms and died.Fibrous exudation in the chest and abdominal cavity was found,and the cardiopulmonary cavity was covered by gel-like substances.The strain was identified as Escherichia coli by its colony morphology,microscopic examination and mass spectrometer identification.The study indicates that the case involves mice infected with Escherichia coli,resulting in thoracoabdominal inflammatory exudative lesions and ultimately leading to the death of the mice.