Fig.1 Colony morphology of isolate on ESBL chromogenic medium (A), MacConkey medium (B) and nutrient broth medium (C)

Fig.2 PCR amplification results of 16S rRNA gene sequences of isolates M, DL2000 DNA marker;1-2, Positive samples; 3, Negative control.

Fig.3 PCR amplification results of sul2 gene in 16 isolates M, DL2000 DNA marker; Lanes 1-16,sul2 gene positive samples; 17, Negative control.

Fig.4 PCR amplification results of TEM gene in 16 isolates M, DL2000 DNA marker; Lanes 1-3, 5-6, 8-10, 13-15, TEM gene positive samples; Lanes 4, 7, 11, 12, 16, Negative samples; 17, Negative control.

Fig.5 PCR amplification results of capsular serotype K5 gene in 16 isolates M, DL2000 DNA marker;Lanes 10, 13, 15, Capsular serotype K5 gene positive samples; Lanes 1-9, 11-12, 14, 16, Negative samples; 17, Negative control.

Fig.6 PCR amplification results of virulence gene mrkD in 16 isolates M, DL2000 DNA marker; Lanes 2-16,Positive samples of virulence gene mrkD; Lane 1,Negative sample; 17,Negative control.

Fig.7 Whole dissection of mice A,No abnormalities in mice under control; B,Gallbladder enlargement, gas accumulation in the intestine, and swelling in mice with weakly virulent strain; C,Obvious gallbladder enlargement, gas accumulation in the intestine, and enlargement in mice with strongly virulent strain.

Fig.8 Morphology of organs in normal mice, as well as virulent mice A, No abnormalities in the lung of mice under control; A1, Congested and enlarged lung in the mice with weakly virulent strain; A2, Obviously congested and enlarged lung in the mice with strongly virulent strain. B, No abnormalities in the spleen of mice under control; B1, Congested and enlarged spleen in the mice with weakly virulent strain; B2, Obviously congested and enlarged spleen in the mice with strongly virulent strain. C, No abnormalities in the liver of mice under control; C1, Congested and enlarged liver in the mice with weakly virulent strain; C2, Obvious congested and enlarged liver in the mice with strongly virulent strain. D, No abnormalities in the kidney of mice under control; D1, Congestion and enlarged kidney in the mice with weakly virulent strain; D2, Obvious congested and enlarged kidney in the mice with strongly virulent strain.

Fig.9 Histopathological changes in virulent mice A, Liver congestion (100×);B, Hepatic nucleopyknosis, neutrophils (400×); C, Thickening of the splenic capsule (100×); D, Necrosis of splenocytes “Starry sky phenomenon” (400×); E, Slightly thickened alveolar diaphragm (100×); F, Lung neutrophils increased (400×); G, Glomerular enlargement, flocculent sedimentation (100×); H, Glomerulus enlargement(400×).