Bacterial Meningitis Caused by Hypervirulent Klebsiella pneumoniae Capsular Genotype K54 with Development of Granuloma-like Nodal Enhancement in the Brain during the Subacute Phase

A 72-year-old man was admitted to the emergency department due to coma. The cerebrospinal fluid cell count was 40,080 cells/μL, and Klebsiella pneumoniae was detected on culture. Stretching the bacterial colonies on an agar plate showed the formation of a viscous string with a length exceeding 5 mm, indicating hypervirulent K. pneumoniae (hv-KP). A genome analysis suggested hv-KP capsular genotype K54 with sequence type 29. Although no brain abscess was detected on contrast-enhanced computed tomography on Day 4 or on magnetic resonance imaging (MRI) on Day 7, contrast-enhanced MRI on Day 23 showed granuloma-like nodal enhancement on the surface of the left insula. Antibacterial therapy was continued until the enhancement disappeared on Day 40. MRI may help determine the duration required for antibacterial therapy. After six months, the patient was discharged and remained free from recurrence.