Salmonella enterica subsp. enterica Serovar Heidelberg Food Isolates Associated with a Salmonellosis Outbreak Have Enhanced Stress Tolerance Capabilities

Abstract

Salmonella enterica serovar Heidelberg is currently the 12th most common serovar of Salmonella enterica causing salmonellosis in the United States and results in twice the average incidence of blood infections caused by nontyphoidal salmonellae. Multiple outbreaks of salmonellosis caused by Salmonella Heidelberg resulted from the same poultry processor, which infected 634 people during 2013 and 2014. The hospitalization and invasive illness rates were 38% and 15%, respectively. We hypothesized that the outbreak strains of Salmonella Heidelberg had enhanced stress tolerance and virulence capabilities. We sourced nine food isolates collected during the outbreak investigation and three reference isolates to assess their tolerance to heat and sanitizers, ability to attach to abiotic surfaces, and invasiveness in vitro. We performed RNA sequencing on three isolates (two outbreak-associated isolates and a reference Salmonella Heidelberg strain) with various levels of heat tolerance to gain insight into the mechanism behind the isolates' enhanced heat tolerance. We also performed genomic analyses to determine the genetic relationships among the outbreak isolates. Ultimately, we determined that (i) six Salmonella Heidelberg isolates associated with the foodborne outbreak had enhanced heat tolerance, (ii) one outbreak isolate with enhanced heat tolerance also had an enhanced biofilm-forming ability under stressful conditions, (iii) exposure to heat stress increased the expression of Salmonella Heidelberg multidrug efflux and virulence genes, and (iv) outbreak-associated isolates were likely transcriptionally primed to better survive processing stresses and, potentially, to cause illness. IMPORTANCE This study provides a deep analysis of the intrinsic stress tolerance and virulence capabilities of Salmonella Heidelberg that may have contributed to the length and severity of a recent salmonellosis outbreak. Additionally, this study provides a comprehensive analysis of the transcriptomic response of S. enterica strains to heat stress conditions and compares baseline stationary-phase gene expression among outbreak-and non-outbreak-associated Salmonella Heidelberg isolates. These data can be used in assay development to screen isolates for stress tolerance and subsequent survival. This study adds to our understanding of the strains associated with the outbreak and informs ongoing regulatory discussions on Salmonella in poultry.

The Prevalence of Salmonella spp. in Two Arctic Fox (Alopex lagopus) Farms in Poland

“…The identified serotypes are commonly encountered in commercial poultry farms which are the primary reservoirs of all Salmonella spp. serotypes in different countries [ 24 , 25 ] and may trigger human infections around the world [ 25 , 26 , 27 ]. The presence of these poultry pathogens in foxes results from feeding these animals with poultry slaughter waste, mainly from turkey processing.…”

A Review of Salmonella and Campylobacter in Broiler Meat: Emerging Challenges and Food Safety Measures

“…However, these mutations appear to be strain or serotype specific. For example, S. Senftenberg 775 W has proven to be extremely heat tolerant [60]. S. Enterica strains have shown significant variation in heat and acid tolerance with log reductions varying between 0.84 and 5.75 log CFU/mL at 57 • C and a pH of 3.0 as seen in Table 2 [61].…”

“…In a multistate outbreak of S. Heidelberg from a single poultry processor, it was determined that isolates possessed enhanced heat tolerance and virulence capabilities [60]. Between 2013 and 2014, reoccurring outbreaks of this enhanced S. Heidelberg were responsible for 634 infections [60]. Current investigations suggest that the persistence or even influx of certain serotypes of Salmonella in poultry is due to plasmids bearing resilient virulence genes that are easily transmissible.…”

“…However, these mutations appear to be strain or serotype specific. For example, S. Senftenberg 775 W has proven to be extremely heat tolerant [ 60 ]. S .…”

“…Enterica strains have shown significant variation in heat and acid tolerance with log reductions varying between 0.84 and 5.75 log CFU/mL at 57 °C and a pH of 3.0 as seen in Table 2 [ 61 ]. In a multistate outbreak of S. Heidelberg from a single poultry processor, it was determined that isolates possessed enhanced heat tolerance and virulence capabilities [ 60 ]. Between 2013 and 2014, reoccurring outbreaks of this enhanced S. Heidelberg were responsible for 634 infections [ 60 ].…”