A 65-year-old man presented to an outpatient clinic with persistent fever for a month and newly onset severe headache. The patient underwent aortic valvuloplasty owing to infective endocarditis with aortic stenosis 28 and 22 years ago, respectively. He had admitted to the hospital for three times with prosthetic valve endocarditis during the previous 11 years and the last episode was placed a year ago. The causative pathogens of each episode were Enterococcus avium, Enterococcus faecalis, and Streptococcus gallolyticus, respectively. Besides, he had diabetes mellitus, hypertension, dyslipidemia, and alcoholic liver cirrhosis as underlying diseases.

On admission, his vital signs were as follows: body temperature, 37.7 ºC; pulse rate, 72/min; respiration rate, 20/min; and blood pressure, 120/80 mmHg. Petechiae were observed on his trunk but no Janeway lesions or Osler’s nodes existed. There was no conjunctival hemorrhage and Roth spot was not detected on ophthalmic examination. Cardiac murmur was not heard on aortic, pulmonary, tricuspid, and mitral area. In addition, neurological deficit including localizing and lateralizing sign was not observed in both upper and lower extremities.

The initial laboratory examination revealed a white blood cell count of 6,600 cells/mm3, hemoglobin of 8.2 g/dL, platelet count of 10⁵×10³ cells/mm³ and C-reactive protein (CRP) level of 5.86 mg/dL. Electrocardiography showed atrial fibrillation with controlled ventricular response and some ventricular premature complexes. Chest and abdomen computed tomography (CT) scans were performed for differential diagnosis of fever, and there was no abnormal finding suggesting infectious syndrome.

On transesophageal echocardiography (TEE), a 1.2 cm sized linear hypermobile structure was found at left ventricular outflow tract. Taking together, these findings with the positive result of blood cultures obtained at the 30 day of fever indicated a diagnosis of prosthetic valve endocarditis; Rothia mucilaginosa was reported from one blood culture bottle among 4 sets of blood culture samples which were collected in BacT/ALERT Aerobic and Anaerobic standard bottles (bioMérieux, Durham, NC, USA) through an automated blood culture system (BacT/ALERT 3D; bioMérieux). Gram-stained smears of cultured media revealed gram-positive cocci in small irregular clusters. The colonies on chocolate agar were whitish to grey in color, non-hemolytic, smooth and mucoid (Fig. 1). The colonies did not grow on the blood agar plate. 16S rRNA sequencing confirmed the species as R. mucilaginosa with 99% of identity. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS; Bruker Daltonics, Billerica, MA, USA) identified the strain as R. mucilaginosa (highest score = 2.092).

At the day of admission, brain magnetic resonance imaging (MRI) was taken for evaluation of headache, which showed multiple microhemorrhages suggesting septic emboli on both hemisphere, corticomedullary junction area and cerebellum.

We started vancomycin, rifampin, and ceftriaxone as an empirical therapy accordingly and the clinical response to the antibiotic therapy was good; his body temperature became normalized and CRP level decreased.

Since no Clinical and Laboratory Standards Institute (CLSI) protocols exist for R. mucilaginosa, we performed antimicrobial susceptibility test using CLSI criteria for staphylococci (M100-S21), as described previously [6]. The result of antimicrobial susceptibility test was reported on hospital day 7 (Table 1), and we changed antibiotic regimen to ampicillin and rifampin.

On hospital day 11, the patient presented gait disturbance with aggravation of headache. Follow-up brain CT and magnetic resonance angiography were performed: newly developed intracranial hemorrhage at left temporal lobe and head of caudate nucleus was observed without vascular malformation such as mycotic aneurysm. Dysphagia and proximal muscle weakness on upper extremities were aggravated gradually and increased size of intracranial hemorrhage was found at follow up brain CT on hospital day 24. After changing antibiotics from ampicillin to vancomycin again, his symptoms were stabilized and there was no progression in neurologic sign.

However, on hospital day 56, the patient’s mental status became stuporous and he was transferred to intensive care unit. Follow-up brain CT showed newly developed intracranial hemorrhage at left parietal region, and intraventricular hemorrhage in both lateral ventricles. The antibiotic regimen was maintained with vancomycin and rifampin and his neurologic symptoms and signs showed waxing and waning. On hospital day 67, he was transferred to general ward and finally was transferred to another hospital for his family’s request on hospital day 75. Right side motor weakness remained as a sequela to the patient.