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

Background: Granulomatous 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.

Methods: The 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.

Results: A 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.

Conclusions: This 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.