A 37-year-old man with a past medical history of AIDS-related lymphoma was admitted to Beijing Youan Hospital on 12 July 2016, for a relapse of diffuse large B cell lymphoma. The patient had been diagnosed with AIDS-related lymphoma 1 year earlier, and received eight courses of chemotherapy with rituximab, doxorubicin, vincristine, and etoposide (R-EPOCH). The patient recovered well and was discharged, with advice for regular follow-up. Three months ago, the results of a positron emission tomography-computed tomography scan suggested lymphoma recurrence, and the patient was transferred to our institution with an indwelling central venous catheter (CVC) catheter that had been inserted 3 months earlier for administration of chemotherapy. After 3 days of chemotherapy with etoposide, ifosfamide, and cisplatin, the results of clinical laboratory tests revealed myelosuppression, with white cell count of 0.11 × 109/L, hemoglobin of 4.0 g/dL, and platelet count of 8 × 109/L. His body temperature had been abnormal for 2 days, reaching 38.6 °C at the highest point, with procalcitonin of 0.96 μg/L, ESR of 56 mm/h, and CD4+ T-lymphocyte count of 52 × 106 cells/L. A physical examination revealed no specific signs of infections or skin manifestations. Two sets of blood cultures, one from a peripheral vein and the other through the CVC (each 10 ml in volume), were collected and sent to the laboratory for examination. The patient was started on empirical antimicrobial therapy with imipenem.
The blood culture drawn through the CVC was first flagged as positive by a BACTEC™ FX instrument (Becton, Dickinson and Company, USA) after 38 h of incubation in an aerobic bottle. After 61 h of culture in an aerobic bottle, the peripheral blood culture also became positive. Direct microscopic examination based on Gram staining revealed the presence of nonsporulating beaded Gram-positive bacilli. Subcultured blood specimens were plated on sheep blood agar and MacConkey agar. On the sheep blood agar incubated at 35 °C in an aerobic environment with 5% CO2, small white colonies became evident within 24 h. After 3 days of incubation, the colonies became mucoid, and the colonies turned yellow-orange. The bacteria were positive for catalase, negative for cytochrome oxidase activity, nonmotile, and unable to grow anaerobically.
Bacterial identification was performed by matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) according to the manufacturer’s instructions, and the obtained protein profiles were processed and analyzed by MALDI Biotyper 3.0 software (Bruker Daltonics, Germany). However, the MALDI-TOF MS failed to confidently identify the isolate to the species level. Nevertheless, the isolate was identified as a Gordonia species, with a top match score of 1.764 (for Gordonia rubripertincta; scores of ≥2.0 and <2.0 to ≥1.7 represent identification to the species level and genus level, respectively), suggesting it did not resemble any known Gordonia species in the database.
Thereafter, bacterial DNA extraction, PCR amplification, and DNA sequencing of the 16S rRNA with a universal primer pair were conducted to confirm the results. The obtained product sequence (1404 bp) was compared with published sequences in the GenBank database (http://www.ncbi.nlm.nih.gov/blast). The results showed that the isolate had 99% matches with the type strains of G. polyisoprenivorans (strains W8130 and VH2), Gordonia bronchialis (strain DSM 43247), and Gordonia terrae (strain EY-T12). Sequencing of the gyrB genes was then performed according to a previous report [4]. The results showed that the gyrB gene of the isolate had 99.0% sequence identity with the gene sequence of the G. polyisoprenivorans strain, indicating that the isolate was G. polyisoprenivorans.
The isolate was sensitive to amikacin, ampicillin, amoxicillin-clavulanate, cefotaxime, imipenem, meropenem, ciprofloxacin, minocycline, linezolid, and vancomycin, with intermediate sensitivity to trimethoprim-sulfamethoxazole.
At 3 days after the start of imipenem therapy, there was a complete disappearance of fever and a remarkable improvement in the patient’s clinical status. From day 5 onward, the patient was switched to oral antibiotics. As there was no swelling or effusion around the CVC, the catheter was not removed. The patient was followed up for 3 months. There was no recurrence of the infection during the follow-up period. However, he died after 3 months apparently from progression of his hematological malignancies.