In 2017, a 60-year-old female presented to her General Practitioner (GP) in Scotland with a slow-healing 1 cm wound on her right finger. She had sustained a minor burn to the finger 9 days prior to her attendance. A swab was taken by the attending clinician. This swab subsequently grew toxigenic  C. ulcerans . This result was telephoned to the out-of-hours local health protection team, 8 days after the case presented to her GP.
The case lived with her partner and owned two German Shepherd dogs. One dog had a history of a long-standing skin complaint, which had been documented as quiescent. The case worked in retail and had no recent travel history. She had not eaten unpasteurized dairy food nor visited any farms within the last 2 weeks. Her most recent diphtheria vaccination was in 2009.
A nose and throat swab were collected from the patient and she was treated with diphtheria vaccine and a 2 week course of clarithromycin. She was excluded from work under the Public Health Act Scotland (2009) until completion of antibiotics and clearance swabs, one from each site (nose, throat and wound) were negative. Four close contacts were identified who required nose and throat swabs to assess for carriage of  C. ulcerans , of whom two were healthcare professionals who had dressed the wound. Contacts were all given diphtheria vaccine and a 1 week course of erythromycin. The two healthcare workers were excluded from work until nose and throat swabs were culture negative. One contact (husband) was identified as carrying  C. ulcerans  in his nose and required a repeat swab following completion of antibiotics to check for clearance. His repeat swab was culture negative. Initial swabs for the fourth contact (a close friend) were negative.
A local veterinary practitioner examined the dogs, which revealed one had an infected skin lesion, which was swabbed. Throat swabs were also collected from both dogs. Toxigenic  C. ulcerans  was recovered in culture from the skin lesion and throat swabs of both dogs. They were commenced on antibiotic therapy and antimicrobial skin wash. Repeat swabs for the dogs were negative following completion of treatment. The dogs were identified as the most likely source of infection, however, it is possible human-human transmission may have occurred.
Wound swab was submitted for routine culture and was inoculated on Columbia blood agar (Thermo-Fisher, Perth, UK). Large numbers of  C.   ulcerans  were cultured and identified using MALDI-TOF (MALDI Biotyper, Bruker, Massachusetts, USA). MALDI-TOF generates unique mass spectrometry profiles, which are compared to a known database of micro-organism profiles, identifying the organism to genus and species levels. The MALDI-TOF score was >2.0, which is an acceptable score for species identification. Susceptibility testing was performed by E-test (bioMerieux) using European Society of Clinical Microbiology and Infectious Disease (EUCAST) interpretative criteria. The isolate was sent to the Diphtheria National Reference Laboratory, Public Health England (PHE), Colindale, London, where the isolates were characterized by genotypic and phenotypic methods. In April 2014, a real-time PCR (qPCR) assay was formally introduced as the front-line test for putative toxigenic corynebacteria to inform public health action. This assay provides confirmation of both identification of C. diphtheriae and  C. ulcerans / C. pseudotuberculosis  and detection of the diphtheria toxin gene. Phenotypic characterization was perfomed by culture on Columbia horse blood, Hoyle's tellurite and Tinsdale agar plates (PHE Media Services, Colindale); API Coryne (bioMerieux) and additional differential biochemical tests (e.g. nitrate reduction, glycogen hydrolysis as required. The modified Elek immunodiffusion test was used to confirm toxin expression. Further genotypic characterization of isolates was performed by MLST as previously described. The clinical isolate from the index case was identified as  C. ulcerans /C.diphtheriae, diphtheria toxin gene positive by qPCR. The species was confirmed as C. ulcerans phenotypically and toxin expression was confirmed by the Elek test. Antimicrobial susceptibility testing results were also confirmed at the reference laboratory and it showed resistance to penicillin and clindamycin but sensitivity to vancomycin, erythromycin, linezolid, ciprofloxacin, doxycycline and rifampicin.  S. aureus  was isolated along with C. ulcerans. S aureus. could be colonizing the skin but was also likely contributing to any skin and soft tissue infection.
  C. ulcerans  was also isolated from a nose swab from the close contact of the index case and this was confirmed as toxigenic  C. ulcerans  as above. Throat swabs from the two dogs and the skin lesion were collected by their veterinary practitioner and submitted to SAC Consulting Veterinary Services laboratory in Inverness where they were cultured on Columbia sheep blood agar and Hoyles tellurite medium (Thermo-Fisher, Perth, UK).  C. ulcerans  was obtained in moderate growth from the throat swabs collected from each dog and in heavy growth from the wound. The wound also contained a heavy growth of  Staphylococcus schleiferi  subsp. coagulans, and an unidentified Gram-positive coccus. Suspect  C. ulcerans  were identified with the API Coryne system. Follow-up samples were collected from the throats of both dogs after treatment was completed and  C. ulcerans  was not detected. Furthermore, the skin lesion had resolved and neither  C. ulcerans , S. schleiferi subsp. coagulans nor the unidentified Gram-positive coccus were detected. The three canine isolates from the two dogs were also confirmed as toxigenic  C. ulcerans .
The six isolates (three human, three canine) were subjected to MLST analysis. Full profiles were not obtained, most likely due to variation in primer binding sites. However, of the partial alleleic profiles obtained (range 2 to 5 out of 7 alleles); all alleles occurring in >1 isolate matched and there were no mismatches, supporting an epidemiological link. All partial allelic profiles obtained (0, 41, 79, 49, 0, 45, 39) were consistent with sequence type 349 (42, 41, 79, 49, 49, 45, 39), which is present in the MLST database (https://pubmlst.org/cdiphtheriae/), from  C. ulcerans  isolated from a cutaneous clinical case in 2005, from Toulouse, France.