Yokenella regensburgei, gram-negative rod of the family Enterobacteriaceae, is a rare human pathogen of unclear clinical significance, potentially opportunistic, given multiple reports within immunocompromised contexts.  A 67-year-old female with a history of well water exposure, aquatic recreational activities, poor hygiene habits, recent diagnosis of primary CNS lymphoma, one month following craniotomy and partial resection, underwent her first chemotherapy cycle. Shortly thereafter, she developed incisional purulence, subsequent weakness and progressive lethargy. Brain imaging revealed an intracranial abscess necessitating drainage; intraoperative cultures grew Y.regensburgei by MALDI-TOF and VITEK2 confirmation. This case describes the first reported incidence of Y.regensburgei intracranial abscess.

MALDI-TOF MS and VITEK2 Automated System were used to confirm identification of the organism from the intraoperative brain abscess specimen.  Antibiotic susceptibility testing was also performed on intraoperative cultures.

MALDI-TOF MS yielded identification of Y.regensburgei with a score of 1.903.   Given the rare occurrence of this organism, a confirmatory identification was performed using the VITEK2 Automated System which identified the organism as Y.regensburgei with 100% probability.

Intraoperative culture susceptibility testing of the current isolate was notable for resistance to ampicillin and cefazolin, with sensitivity to cefepime, ceftriaxone, ciprofloxacin, gentamicin, levofloxacin, meropenem, piperacillin/tazobactam, and trimethoprim/sulfamethoxazole.

Given the multiple risk factors for immunosuppression in the preponderance of known cases worldwide, there is mounting evidence strongly implicating the opportunistic nature of Yokenella regensburgei.  As regards empiric therapy for brain abscess in the specific context of immunosuppression and fresh or well water exposure, it will be paramount to re-evaluate the standard therapy for brain abscess; namely, the potential insufficiency of a third-generation cephalosporin if Yokenella regensburgei is a possible causal organism. Given the successful resolution of infection in the current case, one may consider carbapenems and fluoroquinolones, barring contraindications, as the empiric therapy of choice in such situations.