Human Microbiota Mice: New Animal Models for Enteric Escherichia coli Infections

Abstract

Introduction: Conventional mice are resistant to infection with human enteric bacterial pathogens such as Enterohemorrhagic E.coli (EHEC) and Entertoxigenic E. colli (ETEC). This is, in part, because of host species-specific bacterial virulence factors, but also because of colonization resistance conferred by the normal microbiota of the mouse gut. Our aim was to determine whether gut microbiome composition influences infectivity of mice with either human EHEC or ETEC isolates Methods: C57BL/6'mice with either a mouse microbiome (MMB), or stably colonized with a human gut microbiome (HMB) were gavaged with EHEC strain 86-24 (Stx1, Stx2) or ETEC strain H10407 (ST, LT). Two groups were pretreated with streptomycin (SM) to disrupt their microbiota (MMBsm and HMBsm) before gavage. Mice were observed for weight, signs of infection and fecal shedding of the challenge strain, then euthanized to measure fluid secretion into total gut, small intestine (SI), cecum (CE) and colon (CO) by gut/carcass wt. ratios, and intestinal colonization by 86-24 or H10407 in small intestine and cecum. To define microbiome composition, DNA from fecal pellets was analysed for 16srDNA sequences. Results: For EHEC, a colonic pathogen, secretion was significantly increased over controls in HMB in total gut, SI and CO but was not increased in MMB without SM pretreatment. Secretion was increased to the same degree in SM treated HMbsm and SMBsm mice. Fecal shedding was increased in HMB, but not MMB, mice, as well as in both HMBsm and MMBsm SM-treated mice mice. Colonization was increased in CE and SI of HMB mice vs. MMB mice, and was equally increased in the CE and SI of both MMBsm and HMBsm treated with SM. For ETEC, a small intestinal pathogen, secretion, fecal shedding and colonization of intestinal segments was not observed in either MMB or MMB mice, unless they were treated with streptomycin. The development of intestinal secretion, colonization and fecal shedding in HMB mice challenged with EHEC 86-24 without SM pretreatment occurred without major changes in microbiome composition. In MMB mice increased secretion, colonization and shedding of either EHEC 86-24 or ETEC h10407 required SM treatment which induced major microbiome alteration.s. Conclusion: The presence of a human microbiota in C57BL/6 mice (HMB) rendered the “humanized” mice susceptible to EHEC infection without the need for microbiome disruption with streptomycin. In contrast, a human microbiota was not sufficient to induce susceptibility to infection by ETEC. which required pretreatment with streptomycin. Increased secretion colonization and shedding following EHEC or ETEC challenge of conventional C57BL/6 (MMB) mice was only seen after microbiome disruption with streptomycin. We conclude that a human microbiota in C57BL/6 mice renders them susceptible to infection by the colonic pathogen EHEC 86-24, but not by the small intestinal pathogen ETEC H10407.