Distribution of Pathogenic Bacteria and Analysis of Antimicrobial Susceptibility in Non-Lactation Granulomatous Mastitis Patients.

Background: The aim was to comprehensively explore the distribution of pathogenic bacteria and antimicrobial susceptibility in the breast puncture fluid of the patients with non-lactation granulomatous mastitis to optimize treatment programs.

Methods: Fifteen strains of pathogenic bacteria isolated from the breast puncture fluid of the patients with non-lactation granulomatous mastitis were collected in the breast department, Beijing Hospital of Traditional Chinese Medicine, Capital Medical University from March 2023 to October 2023. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and 16S rRNA sequencing were used to bacterial identi-fication. The E-test method was used to determine the minimum inhibitory concentration (MIC) for each isolate, and the EUCAST standard was used for conducting the antimicrobial susceptibility interpretation. The control lipophilic experiment was performed by adopting the 1% Tween-80 blood plate.

Results: The mean age of 15 patients with non-lactation granulomatous mastitis was 32.73 ± 3.37 years old, of which 14 (93.3%) had a history of pregnancy, and the mean postpartum mastitis was 6.38 ± 9.65 months. MALDL-TOF MS results were consistent with 16S rRNA sequencing by nanopore. Among the isolated fastidious bacteria, there were 15 strains of Corynebacterium kroppenstedtii (CK). These strains showed a high susceptibility rate to rifampicin and ceftriaxone (respectively, 93.3% and 80%). The resistance rate of penicillin was as high as 80%. The resistance rate of ciprofloxacin was 46.7%, and the intermediate rate was 53.3%. The sensitivity rate of moxifloxacin was 53.3%. There were no vancomycin-resistant or linezolid-resistant strains found.

Conclusions: CK plays an important role in the occurrence and development of non-lactation granulomatous mastitis. According to the analysis of clinical antibiotic medication norms and drug sensitivity results, lipophilic rifampicin and linezolid may be the preferred empirical drugs for CK-related non-lactation granulomatous mastitis patients. Meanwhile, the clinical laboratory should endeavor to optimize the culture conditions and use MALDL-TOF MS for accurate identification to improve the detection rate of culture.