Macrolide-responsive histiocytic ulcerative colitis in a French bulldog - clinical and microbiological features - case report

Histiocytic ulcerative colitis (HUC) is a severe chronic enteropathy in dogs, frequently associated with adherent and invasive Escherichia coli (AIEC). This study reports a case of HUC in a French bulldog, unresponsive to enrofloxacin but with full clinical and histopathological remission after azithromycin treatment. The strain isolated from the patient was microbiologically characterized and compared to six other canine-origin strains. All 46 isolates analyzed were multidrug-resistant, and one showed phenotypic ESBL production. Three strains adhered in the presence of D-mannose, and most demonstrated invasiveness in HeLa cells despite the absence of virulence genes. The patient’s isolate (1.4) showed phenotypic characteristics compatible with AIEC, although definitive classification requires genomic sequencing. These findings highlight the importance of bacteriological diagnosis with culture and susceptibility testing to guide appropriate therapy and indicate that the circulation of multidrug-resistant strains in companion animals may pose a potential public health risk within the One Health context.