Abstract
BACKGROUND: Corynebacterium parakroppenstedtii, and C. pseudokroppenstedtii are emerging as significant pathogens in mastitis. Despite its clinical significance, data on its epidemiological, microbiological, and clinical features remain limited. METHODS: We conducted a comprehensive study on mastitis cases associated with Corynebacterium kroppenstedtii complex (CKC) in Guangdong, China (September 2021-September 2023). A total of 101 bacterial isolates were collected and initially identified as CKC using MALDI-TOF MS. Species-level confirmation was achieved through partial sequencing of the 16S rRNA, ropB, and fusA genes. Unclassified isolates were further characterized by whole genome sequencing (WGS). Clinical information was collected, and antimicrobial susceptibility testing was performed. RESULTS: Among the 101cases, C. parakroppenstedtii accounted for 86% of infections, while C. pseudokroppenstedtii for 12%, and a potential novel species for the remaining 2%. Notably, no C. kroppenstedtii infections were detected. Granulomatous lobular mastitis (GLM) was the predominant presentation, occurring in 72% of all cases. Comparative analysis revealed that C. pseudokroppenstedtii infections were associated with higher rates of pus formation and recurrence, whereas C. parakroppenstedtii infections were more prevalent among parous women. Moreover, C. pseudokroppenstedtii exhibited higher resistance rates to ceftriaxone (32.15% vs. 20.00%) and ciprofloxacin (75.00% vs. 19.09%) compared with C. parakroppenstedtii. CONCLUSIONS: These findings challenge the prevailing understanding that C. kroppenstedtii is the main pathogen in mastitis and underscore the need for species-level identification to guide diagnosis and optimize antibiotic therapy for CKC-related mastitis. These insights are vital for improving clinical management and informing treatment strategies.