Antibiotics suppress cell cycle activity in primitive progenitor populations. (A-B) BrdU incorporation was determined for controls (Ctrl) vs antibiotic-treated (Abx) mice in (A) stem cells, (B) MPs, (C) LSK, and (D) primitive progenitor subsets in bone marrow. Results are compiled from 2 independent experiments (n = 9 per group per analysis). (E) Ki67 staining was determined by flow cytometry in the total LSK population. Results are compiled from 3 independent experiments, each performed on pooled marrow from 4 to 5 mice per group. Graphs show mean + SEM. Statistical significance was determined by Student t test. *P < .05, **P < .01.