Human-to-human-transmitted Corynebacterium diphtheriae was historically the main 
pathogen causing diphtheria and has therefore been studied extensively in the 
past. More recently, diphtheria caused by toxigenic Corynebacterium ulcerans is 
an emerging disease in several industrial countries, including the United 
Kingdom, the United States, France, and Germany. However, toxigenic C. ulcerans 
has so far been almost neglected in the development of epidemiologic tools. One 
of the most important tools in modern epidemiology to understand transmission 
pathways is sequence typing of pathogens. Here, we provide a protocol for 
multilocus sequence typing (MLST) to type C. ulcerans strains rapidly and 
relatively cost-effectively. Applying MLST to C. ulcerans for the first time, we 
show that related sequence types (STs) might be associated with the presence of 
the diphtheria toxin gene, which encodes diphtheria toxin (DT), the most 
important diphtheria-causing virulence factor. Interestingly, we found only two 
very closely related STs in the isolates derived from six dogs. Additionally, 
our data show that all STs derived from animals which were at least twice 
present in our analysis were found in humans as well. This finding is congruent 
with zoonotic transmission of C. ulcerans.