A virulent escherichia coli O121-B2-ST131 strain causes hemorrhagic pneumonia in mink: evidence from pathogenicity and animal challenge experiments.

In recent years, rapid fatal hemorrhagic pneumonia (HP) has been increasingly reported in mink. In several studies, the virulence factors of strains isolated from diseased tissues have been identified as extraintestinal pathogenic Escherichia coli (ExPEC). The molecular characteristics of the strains were also analyzed, but whether ExPEC is the etiological agent of HP has not been confirmed in an animal challenge model. In this study, we characterized the antibiotic resistance, virulence characteristics, and pathogenicity of a bacterial strain isolated from a typical case of mink HP, and designated it L1. Our study revealed that isolate L1 has high levels of antibiotic resistance, to multiple antibiotics, including ampicillin, tylosin, kanamycin, and so on. Numerous virulence genes were detected in isolate L1, including those encoding adhesins (focG, afa/draB, mat, crl), invasins (ibeA, einv), and toxin (cnf1). ExPEC isolate L1 belongs to the O121 serogroup and was classified in the B2 phylogroup and sequence type 131 (ST131). Animal experiments showed that L1 is highly pathogenic to mice, and induced fatal HP in mink. A mouse model of isolate L1 infection showed lethargy, depression, and then death. The sick minks showed similar clinical signs and died soon after nasal bleeding and hematemesis, with a large amount of congestion and consolidation in the lungs. Using animal challenge experiments based on Koch's postulates, we demonstrate for the first time that ExPEC is a causative agent of rapid fatal HP in minks. Our research provides important insights into the identification and control of rapid fatal HP in minks and effective antibiotic treatments for infected animals.