Enhanced Actin Pedestal Formation by Enterohemorrhagic Escherichia coli O157:H7 Adapted to the Mammalian Host

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.

Synchronous Disease Kinetics in a Murine Model for Enterohemorrhagic E. coli Infection Using Food-Borne Inoculation

“…For example, host-adapted C. rodentium present in the feces of infected mice are in a hyper-infectious state, i.e., highly transmissible and capable of accelerated colonic colonization, compared to C. rodentium grown in LB (Wiles et al, 2005). EHEC grown in gnotobiotic piglets also exhibit enhanced virulence-related phenotypes (Brady et al, 2011). Thus, in considering ways to develop a consistent and predictable CR(ΦStx 2dact ) infection model, we first revisited the preparation of the inoculum.…”

“…First, because C. rodentium anaerobiosis is associated with enhanced acid-resistance and a transcriptomic profile more similar that of host-adapted, hyper-infectious bacteria (Smith and Bhagwat, 2013), we changed our culturing procedures by growing inocula without shaking. Studies with other enteric pathogens have revealed that the method of inoculum preparation can have dramatic effects on virulence in animal models (Clark et al, 1998; Brady et al, 2011). Second, we infected mice by feeding to avoid potential physical trauma.…”

Actin Pedestal Formation by Enterohemorrhagic Escherichia coli Enhances Bacterial Host Cell Attachment and Concomitant Type III Translocation

“…This enhancement of receptor function by pedestal formation increases overall translocation by increasing bacterial attachment but does not result in enhancement of type III translocation by each bacterium. Upon adaptation to the mammalian host, EHEC translocation of pedestal-promoting (and presumably other T3) effectors into mammalian cells is greatly enhanced per bound bacterium (55). Hence, it will be of interest to investigate the mechanism by which actin pedestal formation promotes bacterial attachment, as well as the (unknown) factors that control the efficiency of EHEC type III translocation.…”

Miniature Swine for Preclinical Modeling of Complexities of Human Disease for Translational Scientific Discovery and Accelerated Development of Therapies and Medical Devices

“…Acute phase proteins associated with innate immune response to infection are often used to distinguish between bacterial and viral infections in swine veterinary practice as done in human medicine (H. Murata, Shimada, and Yoshioka 2004). Swine present symptoms characteristic of human infections and are susceptible to many enteric human pathogens (Andrutis et al 2000;Brady et al 2011;Jeong et al 2010;Sheoran et al 2012;Steele et al 2010;Widmer et al 2000;Yuan et al 1996). Swine are routinely used for studies of infections that burden human populations (Rajao and Vincent 2015) and for developing antibodies and vaccines (Sandbulte et al 2014).…”