Extraintestinal pathogenic Escherichia coli (ExPEC) strains carrying distinct virulence attributes are known to cause diseases in humans and animals and infect organs other than the gastrointestinal tract. A fatal case of bronchopneumonia in a 12-year-old female Quarterhorse was investigated. Following postmortem examination, E coli, Enterococcus sp., and Klebsiella pneumonia were isolated from the lungs, which contained multifocal intra-alveolar accumulations of neutrophils and macrophages with edema, hemorrhage, and fibrin. The strain of E. coli belonged to O2:H21 and carried virulence genes cnf1, sfa, foe, fimA, and papG allele I that are known to be associated with ExPEC strains. The strain was resistant to several antimicrobials including clindamycin, erythromycin, oxacillin, penicillin, and rifampin. This is the first report, to the authors' knowledge, in which ExPEC O2:H21 has been associated with fatal bronchopneumonia in a horse.
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