Clinical metagenomic analysis of bacterial communities in breast abscesses of granulomatous mastitis

•A metagenomic analysis of the microbiota in granulomatous mastitis patients was performed.•Corynebacterium, and in particular Corynebacterium kroppenstedtii, predominated in these patients.•A C. kroppenstedtii-specific qPCR assay was developed, which may be used to guide selective antibiotic therapy.

SummaryBackgroundGranulomatous mastitis (GM) is a chronic inflammatory breast lesion. Its etiology remains incompletely defined. Although mounting evidence suggests the involvement of Corynebacterium in GM, there has been no systematic study of GM bacteriology using -omics technology.MethodsThe bacterial diversity and relative abundances in breast abscesses from 19 women with GM were investigated using 16S rDNA metagenomic sequencing and Sanger sequencing. A quantitative PCR (qPCR) assay was also developed to identify Corynebacterium kroppenstedtii.ResultsA bioinformatic analysis revealed that Corynebacterium was present in the 19 GM patients, with abundances ranging from 1.1% to 58.9%. Of note, Corynebacterium was the most abundant taxon in seven patients (more than a third of the subjects). The predominance of Corynebacterium kroppenstedtii infection (11 of 19 patients, 57.9%) was confirmed with Sanger sequencing and the qPCR assay.ConclusionsThis study profiled the microbiota of patients with GM and indicated an important role for Corynebacterium, and in particular C. kroppenstedtii, in the pathogenesis of this disease.