Abstract:

Objective To observe the bacterial types in cystic neutrophilic granulomatous mastitis (CNGM) samples and analyze the association between the dominant bacterial infections and the histological features in CNGM. Methods Using 16S rRNA gene sequencing and bioinformatics technology, bacterial identification and analysis were conducted on 12 CNGM samples (experimental group) and 5 breast fibroadenoma samples (control group). Paraffin sections were prepared from the 17 lesion tissues and stained with hematoxylin and eosin (HE), Gram staining, acid-fast staining, and PAS staining, followed by observation under light microscopy. The association between bacterial types and pathological features was assessed by combining molecular biology techniques with histological observations. Results Linear discriminant analysis effect size revealed significant differences in abundance between the experimental and control groups, with notable species including Corynebacteriales, Corynebacteriaceae, Corynebacterium, Mesorhizobium, uncultured bacterium, Bradyrhizobium, SHA_109, and Nitrobacter. Further analyses revealed that Corynebacterium kroppenstedtii was detected in 9 cases (9/12) of the experimental group, while none of the control group samples (0/5) showed its presence. This difference was statistically significant (P<0.05). Upon examination of histological sections, among 9 CNGM cases positive for Corynebacterium kroppenstedtii, 6 cases (6/9) showed Gram-positive rods within lipid vacuoles at the center of the granulomas. Both acid-fast staining and PAS staining were negative. No Gram-positive bacteria were found in the tissue samples of the control group. Conclusions Corynebacterium kroppenstedtii was detected in 75% of CNGM lesions, and its localization within lipid vacuoles was closely associated with the formation of surrounding pyogenic granulomas. The presence of Gram-positive rods within lipid vacuoles, combined with the typical granulomatous lesions observed in tissue sections, suggests that Corynebacterium kroppenstedtii may play an important role in the occurrence and development of CNGM.

Key words: Cystic neutrophilic granulomatous mastitis, Granulomatous lobular mastitis, Corynebacterium kroppens-tedtii, 16S rRNA