coliO157:H7 colonisation in adult ruminants did further support the findings of Naylor et al. around the ovine terminal rectum mucosa. Nevertheless, at the end point of the study (day 14), only one lamb hadE. coliO157:H7 micro-colonies associated with the terminal rectum mucosa. A comparison ofE. coliO157:H7 shedding yielded a similar pattern of persistence between rectally and orally inoculated lambs. The ANA-12 inability ofE. coliO157:H7 to effectively colonise the terminal rectum mucosa of all rectally inoculated sheep in the long term, suggests thatE. coliO157:H7 may colonise this site, but less effectively than reported previously for cattle. Keywords:E. coliO157:H7, IVOC, lymphoid, terminal rectum, ovine == 1. INTRODUCTION == EnterohaemorrhagicEscherichia coli(EHEC) O157:H7 is usually a major cause of human gastrointestinal disease that can lead to life-threatening illnesses, such as haemorrahagic colitis and renal failure [13,24]. The main transmission routes for human contamination are through faecal contamination of foods ANA-12 and direct animal contact. Ruminants, especially cattle, are cited as the main reservoir, although small ruminants, such as sheep, have also been implicated [2,3,9,14,23]. As a necessity for the development of optimal intervention strategies, various ruminant studies, mostly in cattle, have reportedE. coliO157:H7 tissue tropisms in the ruminant gastrointestinal tract (GIT). Indeed Grauke et al. [12] first suggested that the lower GIT of orally inoculated cattle and sheep, including the colon, was one location associated withE. coliO157:H7 persistent colonisation. More recently, Naylor et al. [23] showed the lymphoid follicle-dense mucosa at the terminal rectum, as the primary site forE. coliO157:H7 localisation in young calves following oral inoculation. This hypothesis was further assessed by Sheng et al. [26] who exhibited that rectal swab administration ofE. coliO157:H7 resulted in persistent long-term colonisation, thus strongly supporting the terminal rectum mucosa as the preferred site forE. coliO157:H7 colonisation in cattle. A recent feedlotE. coliO157:H7 contamination study generated supportive data suggesting that super-shedder status is linked to greaterE. coliO157:H7 colonisation of the terminal rectum mucosa [5]. Furthermore, necropsy of cattle that were defined as long-term colonised byE. coliO157:H7, revealed that of all GIT sites examined, only the HSPA1A terminal rectum was culture positive forE. coliO157:H7 [17]. Collectively, these data are compelling that in cattle,E. coliO157:H7 colonises the lower GIT effectively, but that long term and high level shedding is dependent upon colonisation of the terminal rectum mucosa. Significantly less is known about the primary site of colonisation forE. coliO157:H7 in sheep, should a single site exist. Interpretation of data from the various oral inoculation studies conducted [6,7,12,15,28] have not identified the terminal rectum as the primary site of colonisation. Indeed, small sparse attaching and effacing (A/E) lesions induced byE. coliO157:H7 have been identified in the ovine colon more readily than at other sites [28]. Using the sameE. coliO157:H7 isolate, our and other laboratories have investigated and hypothesized the role of variousE. coliO157:H7 virulence factors in the well established conventionally weaned 6-week-old lamb model [15,27,29]. Indeed, theE. coliO157:H7 isolate (NCTC12900nalr) previously reported from orally challenged 6-week-old lambs by our laboratory has demonstrated persistent shedding in the faeces [15,28], but detailed bacterial enumeration of the ovine gastrointestinal tract has not been undertaken to determine if the terminal rectum is usually preferentially colonised. For the study to be presented here, in vitro organ culture (IVOC) was initiated to determine if ourE. coliO157:H7 isolate could colonise the ovine terminal rectum mucosa. SinceE. coliO157:H7 rectal inoculation of cattle did demonstrate long-term colonisation in all experimentally infected animals, ANA-12 comparative rectal and oral inoculation studies that encompassed detailed characterisation of the ovine gastrointestinal tract were performed to determine if indeed the terminal rectum was the primary localisation site associated withE. coliO157:H7 persistence in the ovine host. == 2. MATERIALS AND METHODS == == 2.1. Bacterial strain, inocula and reagents == E. coliO157:H7 strain NCTC12900nalris a naturally occurring strain and was previously described and characterised using relevant in vitro and in vivo models [1,15]. It.
