Purpose of review: Most literature that examines gut barrier function focuses on alterations in bacterial flora, changes in mucosal epithelium, or the integrity of the mucosal defenses. This review examines new concepts on the interaction between bacteria and the host, the complex relationships that serve to benefit both in times of health, and the alterations and responses that occur during illness.
Recent findings: Recent work has demonstrated a more complex relationship between bacteria and barrier integrity and between bacteria themselves, which creates a symbiotic relationship beneficial to both host and flora. Host responses alter this balance, inducing changes in bacteria that may be deleterious to both.
Summary: With a better understanding of the bacteria-host interactions in health and the alterations induced by critical illness, new therapies that improve the environment of both may lead to better recovery rates in intensive care unit patients.