An invasive macrolide/lincosamide-resistant Corynebacterium mucifaciens isolate from a patient with diabetic gangrene: Colonies with mucoid appearance harboring a fragment of erm(X)

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Corynebacterium mucifaciens, usually isolated from sterile human specimens, is a rare Corynebacterium species. We describe a blood-origin C. mucifaciens isolate that was resistant to macrolides/lincosamides and had been isolated from a patient with diabetic gangrene. This isolate formed mucoid colonies harboring a fragment of erm(X). As an initial antimicrobial, piperacillin/tazobactam was intravenously administered to the patient for two weeks. Gangrene debridement resulted in good local management. The clinical course was uneventful. The subculture from blood on a blood agar plate revealed mucoid colonies with a positive string test. Gram staining revealed the presence of a mucoid layer around the coryneform. The minimum inhibitory concentrations determined using broth microdilution method indicated resistance to erythromycin/clindamycin. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), 16S rRNA gene sequencing, and antimicrobial resistance (AMR) gene profiling were performed. MALDI-TOF-MS identified this isolate as C. mucifaciens based on its high score (2.22). 16S rRNA gene sequencing revealed 99.3% similarity with DMMZ 2278(T) 16S rRNA gene sequence. AMR gene profiling revealed that this isolate possessed a fragment identical to that of erm(X) from Actinotignum schaalii. MALDI-TOF-MS with 16S rRNA gene sequencing can be useful to identify C. mucifaciens when the coryneform shows a mucoid colony appearance with hyperviscosity.