Abstract

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.

Highlights

  • Corynebacterium (C.) diphtheriae is the type species of the genus and the etiological microorganism of human diphtheria

  • After 24 h of incubation, a poly-bacterial growth was noted in the Newfoundlander including Staphylococcus (St.) schleiferi, Streptococcus (S.) canis, Escherichia coli as well as Acinetobacter baumannii

  • Small coryneform colonies were noted on Columbia sheep blood agar that were preliminarily identified as C. diphtheriae

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Summary

Introduction

Corynebacterium (C.) diphtheriae is the type species of the genus and the etiological microorganism of human diphtheria. And based on DNA homologies, the species C. diphtheriae, C. ulcerans and C. pseudotuberculosis form the C. diphtheriae group and have the potential to cause human infections (Pascual et al 1995; Riegel et al 1995). Most human diphtheria cases in Western Europe are caused by C. ulcerans today (Wagner et al 2010). Systematic changes have led to the description of novel species within the C. diphtheriae group. For one of the four biovars of C. diphtheriae, namely biovar (bv.) Belfanti, species status has been proposed as C. belfantii (Dazas et al 2018). Atypical strains of the same biovar were the subject of another species description, designated as C. rouxii (Badell et al 2020).

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