Chemotherapy is commonly used as myeloablative conditioning treatment to prepare patients for haematopoietic stem cell transplantation (HSCT). Chemotherapy leads to several side effects, with gastrointestinal (GI) mucositis being one of the most frequent. Current models of GI mucositis pathophysiology are generally silent on the role of the intestinal microbiome.

The aim of the study is to identify functional mechanisms by which the intestinal microbiome may play a key role in the pathophysiology of GI mucositis, the investigators applied high throughput DNA-sequencing analysis to identify microbes and microbial functions that are modulated following chemotherapy.

Inclusion Criteria:

• Participants with non-Hodgkin's lymphoma
• Participants receiving the same myeloablative conditioning regimen for five consecutive days, including high-dose Carmustine (Bis-chloroethylnitrosourea), Etoposide, Aracytine and Melphalan.

Exclusion Criteria:

• Patients with a history of Inflammatory Bowel Diseases (IBD), exposed to probiotics, prebiotics or broad-spectrum antibiotics, or administered nasal-tube feeding or parenteral nutrition in the month prior to initiation of the study.

All patients, men and women, 18 to 65, who receive intravenous antibiotics broad spectrum (Tazocilline (piperacillin tazobactam) and Amiklin (amikacin)) in support of the context of febrile neutropenia following a autologous stem cells.