Preliminary comparative genomics analysis among Corynebacterium kroppenstedtii complex necessitates a reassessment of precise species associated with mastitis.

This study focuses on characterizing the first complete genome of *Corynebacterium parakroppenstedtii* and clarifying evolutionary relationships within the *Corynebacterium kroppenstedtii* complex (CKC) through comparative genomics. The researchers sequenced isolate yu01 from a breast specimen and analyzed 35 CKC genomes, identifying a fourth genospecies named *Corynebacterium aliikroppenstedtii*. Traditional single-gene methods (16S rRNA, rpoB, fusA) were found insufficient for precise species identification within CKC due to high genetic similarity and conserved genomic arrangements. The study detected 43 potential virulence genes and 79 species-specific genes, and identified a set of 20 core genes capable of reliably distinguishing CKC species, which may improve identification and epidemiological investigations. Findings suggest that strains previously identified as *C. kroppenstedtii* in mastitis cases are more likely *C. parakroppenstedtii* or *C. pseudokroppenstedtii*, highlighting the need for refined diagnostic methods.