Leptotrichia buccalis bacteremia in patients treated in a single bone marrow transplant unit

We describe four cases of bacteremia due to Leptotrichia buccalis (an organism that is part of the normal human oral flora) that occurred in a bone marrow transplant unit over a 3-month period. All of the patients were neutropenic, all had mucositis or esophagitis, and all were receiving antimicrobial prophylaxis with ciprofloxacin and vancomycin (drugs to which Leptotrichia is resistant). One patient died of adult respiratory distress syndrome; the others had minimal symptoms. Pulsed field gel electrophoresis of bacterial DNA digested with Sma 1 demonstrated a unique banding pattern for each isolate, indicating that the isolates belonged to distinct strains. Quantitative gas-liquid chromatography of whole-cell free fatty acids confirmed the uniqueness of the strains, obviating the need to search for a common source of infection. We postulate that this outbreak resulted from antibiotic selection pressure on the oral flora in patients who had been compromised by severe neutropenia and mucosal disruption.