Abstract
Upon intestinal colonization, enterohemorrhagic Escherichia coli (EHEC) induces epithelial cells to generate actin “pedestals” beneath bound bacteria, lesions that promote colonization. To induce pedestals, EHEC utilizes a type III secretion system to translocate into the mammalian cell bacterial effectors such as translocated intimin receptor (Tir), which localizes in the mammalian cell membrane and functions as a receptor for the bacterial outer membrane protein intimin. Whereas EHEC triggers efficient pedestal formation during mammalian infection, EHEC cultured in vitro induces pedestals on cell monolayers with relatively low efficiency. To determine whether growth within the mammalian host enhances EHEC pedestal formation, we compared in vitro-cultivated bacteria with EHEC directly isolated from infected piglets. Mammalian adaptation by EHEC was associated with a dramatic increase in the efficiency of cell attachment and pedestal formation. The amounts of intimin and Tir were significantly higher in host-adapted than in in vitro-cultivated bacteria, but increasing intimin or Tir expression, or artificially increasing the level of bacterial attachment to mammalian cells, did not enhance pedestal formation by in vitro-cultivated EHEC. Instead, a functional assay suggested that host-adapted EHEC translocate Tir much more efficiently than does in vitro-cultivated bacteria. These data suggest that adaptation of EHEC to the mammalian intestine enhances bacterial cell attachment, expression of intimin and Tir, and translocation of effectors that promote actin signaling.
Highlights
Enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 is the leading cause of outbreaks of bloody diarrhea and is often associated with the triad of hemorrhagic colitis, thrombocytopenia, and renal failure in the United States (Karmali, 1989)
AE lesion formation can be conceptually divided into multiple stages: initial attachment of the bacteria to the host epithelia, type III secretion during which translocated intimin receptor (Tir) and other E. coli secreted proteins (Esps) are translocated into host cells, and Intimin-mediated Tir ligation at the plasma membrane, which triggers host cell signaling events that lead to actin assembly (Donnenberg et al, 1997; Hayward et al, 2006; Frankel and Phillips, 2008; Campellone, 2010)
We found that adaptation of EHEC to the mammalian host is associated with enhanced mammalian cell binding, increased amounts of intimin and Tir, better translocation of functional Tir, and dramatically more efficient pedestal formation on cultured mammalian cells
Summary
Enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 is the leading cause of outbreaks of bloody diarrhea and is often associated with the triad of hemorrhagic colitis, thrombocytopenia, and renal failure in the United States (Karmali, 1989). AE lesion formation can be conceptually divided into multiple stages: initial attachment of the bacteria to the host epithelia, type III secretion during which Tir and other E. coli secreted proteins (Esps) are translocated into host cells, and Intimin-mediated Tir ligation at the plasma membrane, which triggers host cell signaling events that lead to actin assembly (Donnenberg et al, 1997; Hayward et al, 2006; Frankel and Phillips, 2008; Campellone, 2010) Consistent with this model, mammalian cells injected with Esps delivered by a pre-infecting intimin-deficient EPEC mutant are capable of initiating robust actin focusing upon challenge with another strain or particle expressing intimin (Rosenshine et al, 1996; Liu et al, 1999b). We found that adaptation of EHEC to the mammalian host is associated with enhanced mammalian cell binding, increased amounts of intimin and Tir, better translocation of functional Tir, and dramatically more efficient pedestal formation on cultured mammalian cells
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