Antibiotic suppression of bone marrow progenitors is indirect and reversible. (A) Total colony formation was measured for WBM cells incubated for 9 days in methylcellulose in the presence (Abx) or absence (Ctrl) of test antibiotics (VNAM). Results compiled from 2 independent experiments. Graph shows mean + SEM. (B-E) Recovery of cell populations after withdrawal of antibiotics. Peripheral blood cell count recovery was assessed on an automated hematologic cell counter for antibiotic-treated (Abx) mice compared with controls (Ctrl), exemplified by (B) white blood cells and (C) platelets. Bone marrow recovery was assessed by performing (D) whole bone marrow counts and flow cytometry quantification of bone marrow populations, exemplified by (E) total LSK population, in antibiotic-treated mice compared with controls. Graphs show mean ± SEM trend over time (n = 3-4 per group per time point with each time point normalized to the mean of controls for that time point). Single experiment. (F) Sorted LSK cells from controls (Ctrl) and antibiotic-treated (Abx) mice were cocultured with OP9-DL1 cells and cytokines to support T-cell development. Flow cytometry was performed after 14 days in culture to quantify CD3⁺ cells representing lymphoid potential of the sorted LSK cells. The graph shows mean + SEM. (G-H) Controls (Ctrl) and antibiotic-treated (Abx) mice were treated with granulocyte-colony stimulating factor (G-CSF) to assess progenitor response to exogenous stimuli of myeloid differentiation. (G) Peripheral blood granulocyte and (H) total BM LSK response to GCSF. Results are compiled from 2 independent experiments (n = 4-8 per group per analysis). The graphs show mean + SEM. For all panels, statistical significance was determined by Student t test. *P < .05, **P < .01, ***P < .001, ****P < .0001.