Stress response of Salmonella Montevideo adapted to red pepper powders at various humidities and resistance to near-infrared heating

Abstract

In the present study, the stress responses of Salmonella Montevideo adapted to red pepper powder with various humidities were investigated. The resistance of S. Montevideo to near-infrared heating increased significantly when adapted to red pepper powder. Moreover, the pathogen turned to a viable but noncultureable (VBNC) state after storage in red pepper powder at 30 °C with 40 % relative humidity (RH). Therefore, transcriptomic analysis was conducted for pathogens adapted to red pepper powder at 30 °C and 40 % RH for 4 h (VBNC transformation starting point). Compared to the transcriptome from the pathogen grown in tryptic soy broth at 37 °C, a total of 1,268 differentially expressed genes (DEGs) were observed with the criteria of ΙlogFCΙ ≥ 2 and false discovery rate ≤ 0.05, including 229 upregulated and 1,039 downregulated genes. It was confirmed that heat shock protein-related genes such as dnaK and dnaJ were highly overexpressed in the pathogen adapted to red pepper powder. Moreover, genes contributing to the invasion and internalization of S. Montevideo to red pepper powder were upregulated. Finally, higher gene expression levels of the type III secretion system (ssaS, ssaL, sseG, and pipB) with lower sample humidity were observed with quantitative real-time PCR. These results indicated that genomic changes contribute to phenotypic changes, such as heat resistance changes and transformation to the VBNC state.