A Case of Corynebacterium pseudodiphtheriticum Nosocomial Pneumonia

摘要

To the Editor: Corynebacterium pseudodiphtheriticum has seldom been isolated from patients with upper respiratory tract infections and pneumonia. Most reported infections are community acquired and occur in patients with underlying disease and immunosuppression (1). We report a case characterized by hospitalacquired pneumonia in a debilitated patient. Review of the literature indicates that C. pseudodiphtheriticum should be regarded an emerging pathogen. On April 1, 1998, a 68-year-old woman was admitted to the intensive care unit for acute respiratory distress. She had a 14-month history of amyotrophic lateral sclerosis. Three weeks before admission, she had been hospitalized for Staphylococcus aureus pneumonia and had recovered after treatment with amoxicillin and clavulanic acid plus ciprofloxacin. At the time of admission, the patient had a temperature of 38°C. Systolic blood pressure was 120 mm Hg. Ventilation was spontaneous, with respirations 24 per minute; pulmonary sibilants were noted. Respiratory acidosis was also identified, with a pH of 7.35, SaO2 92%, PaO2 60 mm Hg, and PaCO2 60 mm Hg. Laboratory data included 18,000 leukocytes per ml (90% polymorphonuclear cells) and a serum fibrin level of 7 g/L. A chest X-ray showed pneumopathy of the lower segment of the right lung, which was compatible with the diagnosis of inhalation pneumopathy. On day 2 of admission, the patient?s temperature was 39°C, and she had paresis of the vocal cords. After C. pseudodiphtheriticum infection was diagnosed, treatment with intravenous cloxacillin (l g 3 times/day) and amoxicillin plus clavulanic acid (l g 3 times/day) was started. On day 3 after admission, the patient?s breathing worsened, a radiograph showed bilateral pneumopathy, and she was intubated for mechanical ventilation. Two days later, her breathing improved, and a second bronchic aspiration was sterile. The patient eventually died of unrelated complications. Direct microscopy examination of a Gramstained bronchial aspiration sample showed numerous polymorphonuclear cells and grampositive bacilli in parallel rows, which did not show pleomorphism. After 48 hours of incubation at 37°C, 106 colony-forming units/ml of a coryneform bacillus further identified as C. pseudodiphtheriticum grew in pure culture on blood agar gelose (BioMérieux, La Balme les Grottes, France) under a 5% CO2 atmosphere and did not produce hemolysis. The test for catalase was positive, and the following biochemical characteristics were obtained by using a commercial identification strip (ApiCoryne, BioMérieux): absence of carbohydrate fermentation, urea hydrolysis, and nitrate reduction compatible with C. pseudodiphtheriticum. Minimum inhibitory concentrations (disk diffusion method) were 2 mg/L for amoxicillin, 2 mg/L for cefalotin, 0.09 mg/L for doxycycline, 0.03 mg/L for gentamicin, <4 mg/L for vancomycin, 16 mg/L for erythromycin, and 20 mg/L for trimethoprim-sulfamethoxazole. Identification was confirmed by analysis of the cell-wall fatty acid profile by the Sherlock system, by the trypticase soy broth agar database 3.9 (MIDI Inc., Newark, DE), and by 16S rRNA sequence analysis under previously described conditions (2). The 16S rRNA gene sequence was compared with all eubacterial 16S rRNA sequences available in the GenBank database by using the multisequence comparison Advanced Blast NCBI. The sequence had a 99% similarity to that of C. pseudodiphtheriticum (1039/1047 base pairs).