Corynebacterium rouxii, a recently described member of the C. diphtheriae group isolated from three dogs with ulcerative skin lesions.

Corynebacterium (C.) diphtheriae is one of the two etiological pathogens for human diphtheria with significant morbidity and mortality. Recently, members of its biovar Belfanti have been described as two novel species, C. belfantii and C. rouxii. The most important virulence factor and also the premise to cause diphtheria is the isolate's capacity to encode and express the diphtheria toxin (DT). In contrast to C. ulcerans, which represents a potentially zoonotic pathogen, C. diphtheriae (incl. the novel deduced species) has almost exclusively been found to comprise a human pathogen. We here report three rare cases of C. rouxii isolation from dogs suffering from disseminated poly-bacterial exsudative to purulent dermatitis and a traumatic labial defect, respectively. The isolates were identified as C. diphtheriae based on commercial biochemistry and matrix-assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI-TOF MS) analysis. However, recently described specific spectral peaks were highly similar to spectra of C. rouxii, which was confirmed by whole genome sequencing. Further investigations of the dog isolates for the presence of DT by tox gene qPCR revealed negative results. The findings from this study point out that skin infections in companion animals can be colonized by uncommon and so believed human specific pathogens, thereby resembling the clinical signs of cutaneous diphtheria.