Impact of gut colonization by antibiotic-resistant bacteria on the outcomes of autologous stem cell transplantation in multiple myeloma.

Patients undergoing autologous stem cell transplantation (auto-SCT) face elevated risks of infections. Additionally, patients colonized in the gastrointestinal tract with antibiotic-resistant bacteria (ARB) are at higher risk of infection with ARB and other infections. Therefore, patients colonized with ARB before auto-SCT should present with an exceptionally high incidence of infections. According to current literature, ARB colonization is the surrogate marker for dysbiosis, which is known to be associated with a diagnosis of multiple myeloma (MM). Given that, this retrospective study aimed to assess the influence of ARB colonization on infection rates, hematopoiesis regeneration, mucositis, overall survival, and progression-free survival following auto-SCT in MM. Data from 138 MM patients undergoing 141 auto-SCT were analyzed, with 15% showing ARB colonization. Among colonized patients, ESBL-producing gram-negative rods predominated. Patients with gut ARB colonization had significantly higher infection rates than non-colonized individuals (52 vs. 26%, P = 0.02), particularly bloodstream infections (43% vs. 14%, P = 0.004). Colonized patients also tended to exhibit shorter survival rates although there was no statistical significance (1-year and 2-year OS; non-colonized vs. colonized; 97 and 92% vs. 90 and 86%; p = 0.054). Based on our results, gut colonization before auto-SCT negatively affects treatment outcomes.