Rectal Administration of Escherichia coli O157:H7: Novel Model for Colonization of Ruminants

Abstract

Escherichia coli O157:H7 causes hemorrhagic colitis and life-threatening complications. Because healthy cattle are reservoirs for the bacterium, ruminant infection models have applications in analyzing the relationship between cattle and this human pathogen and in testing interventions to reduce or prevent bovine colonization with this bacterium. Current approaches often do not reliably mimic natural, long-term bovine colonization with E. coli O157:H7 in older calves and adult animals (ages that enter our food chain). Based on the recent identification of the bovine rectoanal junction mucosa as a site of E. coli O157:H7 colonization, we developed a novel rectal swab administration colonization model. We compared this method with oral dosing and direct contact transmission (Trojan) methods. E. coli O157:H7 carriage status was determined by fecal or rectoanal mucosa swab culture. High (ϳ10 10 CFU) and low (ϳ10 7 CFU) oral doses of E. coli O157:H7 in sheep and cattle resulted in variable infection with the bacterium. Some animals became colonized with the bacteria and remained culture positive for several weeks, and some animals did not become colonized and rapidly cleared the bacteria in a few days. Pen mates of E. coli O157:H7 culture-positive Trojan cattle had a low infection rate and variable colonization status. However, rectal swab administration of E. coli O157:H7 to cattle resulted in consistent long-term colonization in all animals. The surprising ease with which long-term infections resulted from a single application of bacteria to the rectoanal mucosa also strongly supported this location as a site of E. coli O157:H7 colonization in cattle.Escherichia coli O157:H7 is an enteric pathogen of humans that causes a spectrum of illnesses, including hemorrhagic colitis and renal failure, and can be fatal (14,24,29). Domestic cattle are an important reservoir of this pathogen and are the source for most food-borne infections (8). Experimental and field studies of E. coli O157:H7 in beef and dairy cattle have found within-group variation between individual animals with respect to occurrence and duration of fecal culture-positive status (2,3,6,10,15,17,20,21,27,28). This variation suggests that host factors play an important role in E. coli O157:H7 colonization of cattle. A thorough understanding of the hostbacterium interaction could lead to the development of novel interventions, and in order to investigate interactions between the ruminant host and E. coli O157:H7 researchers must recreate infections in an experimental setting. Moreover, to evaluate the efficacy of traditional types of interventions, such as vaccinations (25), probiotics (4, 5), and antimicrobials, it is necessary to be able to reproduce the state of colonization.The earliest publications of ruminant E. coli O157:H7 inoculation studies reported on the use of very young calves, either preweaned or early postweaning, receiving doses of 10 10 CFU administered orally (6, 10) or through rumen cannulae (16,30). An oral dose of 10 8 CFU given to four ...

Characterization of Haemorrhagic Enteritis in Dairy Goats and the Effectiveness of Probiotic and Prebiotic Applications in Alleviating Morbidity and Production Losses

“…Mature ruminants are considered a reservoir for O157 and non-O157 STECs, with the amount and duration of shedding related to exposure dose [30,31], age [32] and mucosal factors [33]. Despite this information, it is unclear why one animal becomes infected while another does not.…”

Escherichia coli O157:H7-secreted cytotoxins are toxic to enterocytes and increase Escherichia coli O157:H7 colonization of jejunum and descending colon in cattle

“…In contrast, Shiga toxins do not affect either EHEC O157:H7 colonization of the terminal rectum in single strain rectal challenged cattle (Sheng et al 2006) or secretory responses in bovine ileal intestinal loops from older calves (Stevens et al 2002). The terminal rectum studies (Naylor et al 2003;Sheng et al 2004Sheng et al , 2006Low et al 2005;Lim et al 2007) have focused on the role of lymphoid tissue in the EHEC O157:H7 infection process in cattle without comparisons with absorptive epithelium in other intestinal sites despite the reported association of EHEC O157:H7 with small and large intestinal sites in challenged cattle (Cray and Moon 1995;Grauke et al 2002;Van Baale et al 2004). In a previous study, we reported that there were no differences in the dose-dependent colonization of small and large intestinal sites compared with the terminal rectum (Baines et al 2008, manuscript in preparation) and in this study, we add to this by showing that the small and large intestinal tissues also respond to EHEC O157:H7 secreted cytotoxins in a similar manner to that reported for a model system purported to better represent the response of ruminant systems to EHEC O157:H7 colonization (Robinson et al 2006).…”

“…These shedding patterns were suggested by Grauke et al (2002) to represent differences in EHEC O157:H7 colonization, and we recently confirmed this hypothesis (Baines et al 2008, manuscript in preparation). Other factors affect EHEC O157:H7 colonization in cattle including age (Cray and Moon 1995) and exposure dose (Besser et al 2001;Sheng et al 2004). Two EHEC effector molecules, Intimin and Tir, are important EHEC O157:H7 virulence factors, enhancing the magnitude and duration of shedding in calves and cattle (Dean-Nystrom et al 1998;Stevens et al 2002;Sheng et al 2006;Sinclair et al 2006) with the benefit derived from their involvement in the intimate attachment of bacteria to mucosal tissues.…”

“…The current study was directed at determining whether EHEC O157:H7-secreted cytotoxins could contribute to the shedding patterns observed for challenged cattle. Many studies have examined the EHEC O157:H7 shedding patterns in challenged older calves and cattle (Cray and Moon 1995;Brown et al 1997;Besser et al 2001;Grauke et al 2002;Sheng et al 2004;Bach et al 2005;McAllister et al 2006) with three patterns of EHEC colonization evident: non-persistent, cattle shedding for about a week; moderately persistent, cattle shedding for about 1 mo; and persistent, cattle shedding for 3 mo to a year (Grauke et al 2002). These shedding patterns were suggested by Grauke et al (2002) to represent differences in EHEC O157:H7 colonization, and we recently confirmed this hypothesis (Baines et al 2008, manuscript in preparation).…”

“…EHEC O157:H7 has been isolated from the small and large intestine of older calves and mature cattle but not necessarily associated with A/E lesions (Cray and Moon 1995;Brown et al 1997;Grauke et al 2002;Naylor et al 2003;van Baale et al 2004). The current model for EHEC O157:H7 colonization in cattle suggests that the lymphoid-follicle dense mucosa in the terminal rectum is the primary colonization site and it is this colonization that is responsible for persistent shedding (Naylor et al 2003Sheng et al 2004Sheng et al , 2006Lim et al 2007). The basic assumption of this model is that cattle are not adversely affected by EHEC O157:H7 virulence factors, and although a reduction in the expression of some EHEC O157:H7 virulence factors has been demonstrated (Rashid et al 2006), it is not true for all virulence factors.…”