Fig. 1

Disruption of the intestinal microbiota during cancer chemotherapy. Under normal circumstances (left), the healthy and diverse bacterial microflora and the host tissues promote stability and colonization resistance, preventing expansion of potential pathogens. Systemic chemotherapy (right) leads to mucosal barrier injury (mucositis). During this time, the microbiota is also disrupted, possibly by chemotherapy or by antibiotics that are given simultaneously, or because of decreased host control over microbial populations, or expansion of a pathogenic species due to mucosal inflammation. The microbiota is dominated by a single pathobiont, which can escape into the systemic circulation by translocation through damaged epithelial tissues. Spread beyond mesenteric lymph nodes particularly occurs as a result of failure of systemic immune defenses