Genomic and Phenotypic Signatures of Corynebacterium Kroppenstedtii complex in Non-Puerperal Mastitis

Corynebacterium Kroppenstedtii complex are increasingly recognized as important pathogens in non-puerperal mastitis, particularly in granulomatous forms, yet their species-level characteristics and clinical significance remain poorly defined. Here, we analyzed 13 CKC isolates from patients with the non-puerperal mastitis, using phenotypic, biochemical, antimicrobial susceptibility and whole-genome approaches. Species identification revealed C. parakroppenstedtii n = 7,as the predominant isolate, followed by C. kroppenstedtii n = 4,and C. pseudokroppenstedtii n = 2. All isolates displayed limited metabolic activity and were uniformly susceptible to intravenous agents such as vancomycin and linezolid. In contrast, multidrug resistance to macrolides, lincosamides, fluoroquinolones, and tetracyclines was predominantly observed in C. kroppenstedtii and C. pseudokroppenstedtii. Whole-genome sequencing identified a conserved set of 26 resistance and 44 virulence-associated genes across isolates, while one C. parakroppenstedtii strain uniquely carried ESX-3 and Hemolysin III, suggesting species-specific pathogenic potential. These findings underscore the genomic diversity and resistance burden of CKC in non-puerperal mastitis, highlighting the importance of precise microbiological identification and tailored antimicrobial strategies in clinical management.