In this prospective study, the primary objective will be to investigate the association between the use of antibiotics administered during the admission period of Stem cell transplant (SCT) and the rate of overall change in microbiota composition across adjacent samples in time.

Early preclinical studies suggested that intestinal microflora contribute to aGVHD and may be relapse. There is increasing evidence that use of antibiotics may have a detrimental impact on intestinal microbiota composition and, consequently, the outcome of SCT.However, effect on different antibiotic prophylaxis regimens and broad-spectrum antibiotics used during transplant and the intestinal microbiota composition and hence adverse outcomes are not known. Stool samples will be collected from patients who are undergoing SCT at:

1. preconditioning
2. at day 0 (stem cell infusion)
3. once in the period of day + 7-10 post SCT
4. once first day or second day of BMT OPD clinic visit
5. once if they develop >=grade I GVHD
6. once at time of recovery from GVHD

Inclusion Criteria:

• Patients aged 18-80 years
• patients undergoing allogenic or autologous SCT for malignant hematological conditions or bone marrow failure

stem cell transplant patients