Enterobacter cloacae inhibits human norovirus infectivity in gnotobiotic pigs.

Shaohua Lei,Mariah Weiss,Guohua Li,Lijuan Yuan,Xingdong Yang,Xi Jiang,Helen Samuel,Tammy Bui,Erica Twitchell,Ashwin Ramesh,Ke Wen

doi:10.1038/srep25017

Abstract

Human noroviruses (HuNoVs) are the leading cause of epidemic gastroenteritis worldwide. Study of HuNoV biology has been hampered by the lack of an efficient cell culture system. Recently, enteric commensal bacteria Enterobacter cloacae has been recognized as a helper in HuNoV infection of B cells in vitro. To test the influences of E. cloacae on HuNoV infectivity and to determine whether HuNoV infects B cells in vivo, we colonized gnotobiotic pigs with E. cloacae and inoculated pigs with 2.74 × 104 genome copies of HuNoV. Compared to control pigs, reduced HuNoV shedding was observed in E. cloacae colonized pigs, characterized by significantly shorter duration of shedding in post-inoculation day 10 subgroup and lower cumulative shedding and peak shedding in individual pigs. Colonization of E. cloacae also reduced HuNoV titers in intestinal tissues and in blood. In both control and E. cloacae colonized pigs, HuNoV infection of enterocytes was confirmed, however infection of B cells was not observed in ileum, and the entire lamina propria in sections of duodenum, jejunum, and ileum were HuNoV-negative. In summary, E. cloacae inhibited HuNoV infectivity, and B cells were not a target cell type for HuNoV in gnotobiotic pigs, with or without E. cloacae colonization.

Highlights

In vivo evidence is essential to test the stimulatory role of E. cloacae and to confirm that B cells are a natural target for robust Human noroviruses (HuNoVs) infection and replication
No significant difference in the incidence of diarrhea was observed among groups at any time points (Table 1), indicating E. cloacae colonization did not affect the incidence of diarrhea in Gn pigs after HuNoV infection
These data demonstrated that E. cloacae colonization inhibited HuNoV shedding in Gn pigs

Summary

Introduction

HuNoV pathogenesis studies and vaccine evaluations in Gn pigs have high translational relevance to those of humans[13,14,23]. Compared to chimpanzees (no longer available for biomedical research) and immunodeficient mice, Gn pigs are currently preferable for HuNoV infection study in many ways, such as the ability to become infected via oral route and resulting in diarrhea and fecal virus shedding[24]. Via E. cloacae colonization in the well-established neonatal Gn pig model of HuNoV infection and diarrhea, we aimed to (i) elucidate the effects of E. cloacae on HuNoV infectivity in vivo, (ii) determine whether HuNoV infects B cells in vivo, and (iii) explore the mechanism of altered HuNoV infectivity in the presence of E. cloacae

Objectives

Methods

Results

Conclusion