Characterization of a Multidrug-Resistant Salmonella enterica Serovar Heidelberg Outbreak Strain in Commercial Turkeys: Colonization, Transmission, and Host Transcriptional Response.

Bradley L Bearson,Shawn M D Bearson,Daniel C Shippy,Torey Looft,Guohong Cai

doi:10.3389/fvets.2017.00156

Abstract

In recent years, multidrug-resistant (MDR) Salmonella enterica serovar Heidelberg (S. Heidelberg) has been associated with numerous human foodborne illness outbreaks due to consumption of poultry. For example, in 2011, an MDR S. Heidelberg outbreak associated with ground turkey sickened 136 individuals and resulted in 1 death. In response to this outbreak, 36 million pounds of ground turkey were recalled, one of the largest meat recalls in U.S. history. To investigate colonization of turkeys with an MDR S. Heidelberg strain isolated from the ground turkey outbreak, two turkey trials were performed. In experiment 1, 3-week-old turkeys were inoculated with 108 or 1010 CFU of the MDR S. Heidelberg isolate, and fecal shedding and tissue colonization were detected following colonization for up to 14 days. Turkey gene expression in response to S. Heidelberg exposure revealed 18 genes that were differentially expressed at 2 days following inoculation compared to pre-inoculation. In a second trial, 1-day-old poults were inoculated with 104 CFU of MDR S. Heidelberg to monitor transmission of Salmonella from inoculated poults (index group) to naive penmates (sentinel group). The transmission of MDR S. Heidelberg from index to sentinel poults was efficient with cecum colonization increasing 2 Log10 CFU above the inoculum dose at 9 days post-inoculation. This differed from the 3-week-old poults inoculated with 1010 CFU of MDR S. Heidelberg in experiment 1 as Salmonella fecal shedding and tissue colonization decreased over the 14-day period compared to the inoculum dose. These data suggest that young poults are susceptible to colonization by MDR S. Heidelberg, and interventions must target turkeys when they are most vulnerable to prevent Salmonella colonization and transmission in the flock. Together, the data support the growing body of literature indicating that Salmonella establishes a commensal-like condition in livestock and poultry, contributing to the asymptomatic carrier status of the human foodborne pathogen in our animal food supply.

Highlights

Food-producing animals such as swine, cattle, and poultry are a major reservoir of the human foodborne pathogen Salmonella [1, 2]
Using Bonferroni’s multiple comparison test, no significant difference in average body temperatures at 1, 2, or 3 dpi compared to pre-inoculation was observed at either inoculation dose; no fever was induced in the turkeys following S
In our experience with challenging swine or turkeys with various Salmonella serovars, we typically observe a considerable decrease in Salmonella CFUs for fecal shedding and tissue colonization by 7 dpi compared to the initial inoculation dose, not an increase as measured in this study

Summary

INTRODUCTION

Food-producing animals such as swine, cattle, and poultry are a major reservoir of the human foodborne pathogen Salmonella [1, 2]. While some Salmonella serovars can cause disease in food-producing animals, most serovars colonize these animals asymptomatically, resulting in the hosts becoming carriers and intermittent shedders of Salmonella [1]. The prevalence of foodborne disease outbreaks caused by Salmonella enterica serovar Heidelberg Heidelberg in 2011 that caused 136 confirmed cases of human foodborne disease (39% hospitalization rate) and the recall of 36 million pounds of ground turkey meat [5,6,7]. Heidelberg isolates were from human bloodstream infections with resistance to one or more antimicrobial agents being associated with increased risk for invasive disease [10]. Heidelberg isolates that cause human foodborne disease are MDR [13]. Heidelberg thereby leading to the recent outbreaks with this human foodborne pathogen

MATERIALS AND METHODS

RESULTS AND DISCUSSION

ETHICS STATEMENT