Breakthrough bacteremia due to Clostridium tertium in a patient with neutropenic fever, and identification by MALDI-TOF mass spectrometry

Clostridium tertium is rare in a human clinical specimen and its pathogenicity is often uncertain. However, the organism has been increasingly recognized as a cause of bacteremia and other infections in immunocompromised patients, especially those with hematologic malignancies. The diagnosis and treatment of C. tertium are difficult due to its growth pattern, micromorphology, and antibiotic resistance. The organism can easily be misidentified as Gram-positive aerobic rods such as Bacillus species, usually considered as a contaminant. Furthermore, it is not covered by empirical treatment with many broad-spectrum antibiotics. Here we report a case of breakthrough bacteremia due to C. tertium that occurred in a patient with acute leukemia and neutropenic fever, who was treated with an empirical regimen of ceftazidime and amikacin. The bacterium was rapidly identified by new mass spectrometry technology (MALDI-TOF MS) and the patient recovered under meropenem and vancomycin treatment, without complications.