The effect of new broad-spectrum antibiotics on faecal flora of cancer patients

The effects of newly available broad-spectrum antibiotics, used for infection prophylaxis and therapy in cancer patients, on faecal aerobic and anaerobic bacteria were investigated. Quantitative and qualitative aerobic and anaerobic cultures were performed in 34 patients before therapy and between the sixth and eleventh day of therapy. Of the two prophylactic regimens norfloxacin plus amphotericin-B eliminated Enterobacteriaceae and enterococci without encouraging growth of yeasts or Clostridium difficile whereas trimethoprim-sulphamethoxazole did not eliminate enterococci and colonization with toxin producing C. difficile occurred in two of ten patients. The effect of the two infection prophylaxis regimens on counts of faecal anaerobes was comparable. Monotherapy with ceftazidime and combination therapy with ceftazidime plus tobramycin did not result in major changes ( ≥ 3 log increase or decrease) in faecal anaerobic bacteria. Enterobacteriaceae were eliminated except in one patient treated with ceftazidime. The effect of these therapeutic regimens on enterococci was variable. Colonization by yeasts or by toxin negative C. difficile (two of three patients) were found in the ceftazidime group only. During combination therapy with piperacillin plus amikacin for fever during granulocytopenia signs of a disturbed faecal flora were found in one of three patients. Changes in faecal anaerobic bacteria were most marked in the ceftazidime plus piperacillin group. Moreover the isolation of a toxin positive C. difficile occurred in this group, in a patient who was colonized with toxin negative C. difficile before treatment. The other therapeutic antibiotic regimens (ceftazidime alone, ceftazidime plus tobramycin and piperacillin plus amikacin) did not have a profound effect on the faecal flora and may disturb colonization resistance less than the double β-lactam combination.