A hidden pathogen in routine cultures: Recurrent bilateral breast abscesses caused by Corynebacterium kroppenstedtii.

Corynebacterium kroppenstedtii is an increasingly recognized but frequently overlooked opportunistic pathogen strongly associated with granulomatous mastitis. Due to its unique lipophilic nature, it exhibits slow growth on standard media, often leading to false-negative results in routine laboratory settings. We present a 38-year-old female patient with recurrent bilateral breast abscesses completely unresponsive to standard empirical antibiotic therapy. Despite dense polymorphonuclear leukocytes observed in initial Gram stains of the abscess, routine cultures initially remained negative. Accurate identification was successfully achieved after extended incubation using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) and 16S rRNA gene sequencing. Resolution was attained via a multidisciplinary approach and a prolonged regimen of targeted lipophilic antibiotics. This case underscores the necessity of considering C. kroppenstedtii in refractory bilateral breast abscess to facilitate timely identification, preventing recurrences and potential complications.