Salmonella Hessarek: An emerging food borne pathogen and its role in egg safety

Abstract

In Australia and other parts of the world, contaminated eggs or egg-containing food products are common vehicles for human Salmonella outbreaks. Recently, an uncommon serotype, Salmonella Hessarek, has emerged in foodborne salmonellosis due to the consumption of contaminated eggs and egg products. Limited research is available on the behaviour of Salmonella Hessarek in eggs. Therefore, this study was performed to understand the penetration ability and transcriptional behavior of Salmonella Hessarek in table eggs stored at different temperatures. The assay revealed that the penetration ability of Salmonella Hessarek was significantly (P < 0.05) affected by the egg storage temperature. Salmonella penetration into egg contents was significantly higher in cold (collected 3 h post-oviposition) compared with warm (collected immediately post-oviposition) eggs stored at 25 °C. There was 4 and 2.39 log increase in Salmonella cells in yolk and albumen, respectively, of the eggs stored at ambient temperature. The gene expression data indicated that genes regulate the pathways involved in stress and metabolism, such as yafD, proP, rpoS, phoP, adkF, and purG were significantly upregulated in yolk and on the eggshell surface, at refrigerated temperature. The gene expression data suggested that at refrigerated temperature, Salmonella Hessarek maintained its cell viability through upregulating the key genes necessary for survival. The findings further showed that not all genes involved in the vital functions of Salmonella were consistently regulated at 5 °C and 25 °C in different egg contents. This study revealed that Salmonella Hessarek has the capacity to penetrate and survive in eggshell pores. Storage of eggs at refrigerated temperature can reduce the penetration and replication risk of Salmonella Hessarek in eggs.