The Bacterial Swiss Army Knife: ExPEC Utilizes Multiple Resistance Mechanisms to Counteract Host Immune Responses

Extraintestinal pathogenic <i>Escherichia coli</i> (ExPEC) is a major cause of infections of the urinary tract, the bloodstream, and other non-intestinal sites in humans. ExPEC often resists the bactericidal action of human immune defenses including complement, antimicrobial peptides, antibodies, and cell-mediated killing. This review provides an overview of the main host defense strategies, and the mechanisms and molecules ExPEC engages to resist these human immune responses. Surface-exposed polysaccharides, outer membrane proteins, cytotoxins, and proteases are all part of the bacterial arsenal of defenses that can neutralize many of the host's immune defenses. These factors work in concert to enable ExPEC to survive and thrive in extraintestinal environments of the human body.