: an overlooked cell invader.

SUMMARY and are human pathobionts that exhibit a dual lifestyle as commensal and pathogenic bacteria. The pathogenic lifestyle is associated with specific conditions involving host susceptibility and intestinal overgrowth or the use of a medical device. Although the virulence of appears to benefit from its antimicrobial resistance, is recognized for its higher pathogenic potential. has long been considered a predominantly extracellular pathogen; it adheres to and is taken up by a wide range of mammalian cells, albeit with less efficiency than classical intracellular enteropathogens. Carbohydrate structures, rather than proteinaceous moieties, are likely to be primarily involved in the adhesion of to epithelial cells. Consistently, few adhesins have been implicated in the adhesion of to epithelial cells. On the host side, very little is known about cognate receptors, except for the role of glycosaminoglycans during macrophage infection. Several lines of evidence indicate that internalization may involve a zipper-like mechanism as well as a macropinocytosis pathway. Conversely, can use several strategies to prevent engulfment in phagocytes. However, the bacterial and host mechanisms underlying cell infection by are still in their infancy. The most recent striking finding is the existence of an intracellular lifestyle where can replicate within a variety of host cells. In this review, we summarize and discuss the current knowledge of -host cell interactions and argue on the need for further mechanistic studies to prevent or reduce infections.