Recovery of murine myelopoiesis after cytostatic reduction by Ara-C. Effect of bacitracin-induced changes in the intestinal microflora and influence of timing.

The influence of intestinal flora modulation by oral bacitracin on the recovery of myelopoiesis after Ara-C was studied in C3H/Law mice. Bacitracin resulted in a 3-5 log increase of Gram-negative bacteria and a 10-fold increase of the intestinal endotoxin concentration. Initiation of bacitracin before Ara-C stimulated the initial rebound increase of colony-forming units for granulocytes and macrophages (CFU-GM) from 23.2 +/- 1.3 to 28.4 +/- 1.4 x 10(3) per femur. Starting the bacitracin after Ara-C advanced the second phase of the rebound CFU-GM increase with 6 days. An important role in the recovery of myelopoiesis after cytostatic drugs in C3H/Law mice is suggested for the intestinal Gram-negative microflora, probably mediated by bacterial endotoxin.