The "clostridial effect" of selective decontamination of the human gut with trimethoprim/sulphamethoxazole in neutropenic patients.

During 59 periods of hospitalisation, 39 patients with either acute myeloid leukemia (22), acute lymphatic leukemia (9), acute undifferentiated leukemia (1), blastic crisis of chronic myeloid leukemia (6) or high-grade malignant non-Hodgkin lymphoma (1) were subjected to aggressive polychemotherapy after selective decontamination of the gut. The patients were given an amphotericin B suspension in a dosage of 1.2 g/day for two days, after which one tablet of trimethoprim/sulphamethoxazole (TMP/SMZ) (160 mg TMP and 800 mg SMZ) t.i.d. was added to prevent endogenous infections by gram-negative aerobic bacteria or moulds and to maintain the "colonisation resistance" endowed by the anaerobes. During 16 of the 59 periods of hospitalisation, no potentially pathogenic aerobic bacteria were isolated. TMP/SMZ-resistant Escherichia coli were the etiological agent of septicemia in two patients, and resistant Klebsiella pneumoniae and Pseudomonas aeruginosa in two other patients. These bacteria were cultured from the patients' fecal samples prior to the development of septicemia. We observed that long-term prophylaxis with TMP/SMZ modified the normal aspect of the fecal biotop culture, not only by suppressing the aerobic gram-negative bacteria, but also by allowing certain clostridia to appear. We differentiated 207 clostridia from the fecal samples of 29 patients and observed a predominance of TMP/SMZ-resistant Clostridium difficile, Clostridium innocuum and Clostridium clostridiiforme. C. difficile was also isolated from the blood culture of a neutropenic patient treated with TMP/SMZ and proved to be very toxic in the Verocell culture.