Rothia mucilaginosa Pneumonia Diagnosed by Quantitative Cultures and Intracellular Organisms of Bronchoalveolar Lavage in a Lymphoma Patient
A 46-yr-old woman was diagnosed with B lymphoblastic lymphoma stage IVB on December 6, 2011. She achieved complete remission after 2 courses of chemotherapy that comprised vincristine, prednisolone, daunorubicin, and L-asparaginase. In January 2012, she was treated with ciprofloxacin because of neutropenia and bacteremia caused by Bacillus cereus. On February 18, 2012, fever and diarrhea developed after the second course of chemotherapy, and she received empirical treatment with vancomycin for 4 days and meropenem for 8 days. On February 22, 2012, Clostridium difficile-associated diarrhea developed, and oral metronidazole was administered for 7 days. The patient was admitted to the hospital on March 6, 2012 for scheduled chemotherapy.\nOn admission, her body temperature was 36.0℃, pulse rate was 101/min, respiration rate was 20/min, and blood pressure was 111/76 mmHg. Complete blood cell count showed a hemoglobin level of 9.6 g/dL, a white blood cell count of 7.5×109/L (with 1.0% myelocytes, 2.0% metamyelocytes, and 54.0% neutrophils), and a platelet count of 351×109/L. The C-reactive protein level was elevated at 0.1 mg/dL. The chest radiograph and computed tomography (CT) scan revealed multifocal nodular and patchy consolidation in both the lungs that suggested atypical pneumonia or bronchiolitis obliterans organizing pneumonia secondary to drug reaction or viral infection (). The abdominal CT scan revealed a liver abscess in liver segment III. Due to suspicion of community-acquired atypical pneumonia, she was treated empirically with levofloxacin for 7 days and underwent bronchoscopy on hospital day (HD) 3.\nThe BAL specimen was used for the quantitative culture, and a gram-stained smear was prepared with a cytospin centrifuge. Microscopy of the smear revealed a white blood cell count of 10-25/low power field (LPF), an epithelial cell count of <1/LPF, and 7% of leukocytes contained intracellular organisms (ICOs) (). Acid-fast bacilli stain and culture, Mycobacterium tuberculosis PCR, respiratory virus PCR, and fungus culture of the BAL specimen were all negative, but the patient was positive for rhinovirus. The quantitative cultures of the BAL specimen on blood agar plates and chocolate agar plates grew predominantly mucoid, non-hemolytic, and grayish convex colonies after 2 days of incubation at 37℃ and 5% CO2 (). The colony counts were approximately 200,000 colony-forming units (CFU)/mL. The colonies were sticky on the agar surface. Gram staining of the colonies showed gram-positive cocci of the same morphology as those that appeared on the direct smear (). The bacterium was identified as R. mucilaginosa using an API Staph Identification Panel (bioMérieux SA, Marcy 1'Etoile, France); the profile number was 6310134 at a probability of 99.9%. The 16S rRNA gene sequencing of this isolate showed an identity of 99.7% (1,325 of 1,329 bp) with R. mucilaginosa ATCC 25296T (GenBank accession no. ACVO01000020). The isolate also had 98.3% homology with R. dentocariosa ATCC 17931T (GenBank accession no. CP002280).\nThe minimum inhibitory concentrations (MICs) for this isolate were determined using a MicroScan MICroSTREP plus 1 panel (Siemens Healthcare Diagnostics, West Sacramento, CA, USA). This broth microdilution susceptibility test was performed with cation-adjusted Mueller-Hinton agar, supplemented with 3% lysed horse blood (Siemens Healthcare Diagnostics) []. MICs of the tested antimicrobials were 0.06 µg/mL for penicillin, 0.06 µg/mL for ampicillin, ≤0.5/0.25 µg/mL for amoxicillin/clavulanate, ≤0.25 µg/mL for azithromycin, >0.5 µg/mL for clindamycin, ≤0.06 µg/mL for erythromycin, 2 µg/mL for chloramphenicol, ≤0.25 µg/mL for ceftriaxone, 1 µg/mL for cefaclor, ≤0.25 µg/mL for cefotaxime, 2 µg/mL for cefepime, ≤0.25 µg/mL for cefuroxime, >4 µg/mL for levofloxacin, >0.5 µg/mL for meropenem, 0.5/9.5 µg/mL for trimethoprim/sulfamethoxazole, 1 µg/mL for tetracycline, and 1 µg/mL for vancomycin. The MICs of other antimicrobials were determined using the E-test (AB Biodisk, Solna, Sweden) on Mueller-Hinton agar supplemented with 5% sheep blood; the MICs were 12 µg/mL for gentamicin, 0.19 µg/mL for imipenem, and 0.5 µg/mL for piperacillin/tazobactam.\nIntravenous levofloxacin treatment was stopped on HD 7 because of the possibility of leukopenia induced by antibiotic therapy. The chest radiograph obtained at this time showed a reduction in the multifocal nodular and patchy consolidation in both lungs. Ampicillin/sulbactam and ciprofloxacin were started due to the organizing liver abscess. On HD 30, the third course of chemotherapy was started and completed without complications. The patient was discharged on HD 46 with complete resolution of pneumonia and liver abscess.