Transcriptomic Analysis of <i>Salmonella enterica</i> Newport Adaptive Response to Oxidative Antimicrobials

Agricultural water systems are a known potential source for contamination of fresh produce with foodborne pathogens including Listeria monocytogenes, pathogenic Escherichia coli, as well as Salmonella enterica strains. To reduce this associated risk, antimicrobials such as hypochlorite compounds and peroxyracetic acid (PAA) have been utilized as in-line irrigation disinfectants and as post-harvest treatments. These treatments are considered effective and commonly used; however, pathogenic microbes like Salmonella have the ability to adapt to many environmental conditions. Adaptive response to environmental factors like oxidative conditions, contributes to transfer, attachment, and resilience of Salmonella on surfaces. Through RNA sequencing and analysis of the obtained transcriptome, adaptive response of Salmonella to hypochlorite and PAA can be quantitatively evaluated. Within this study, an outbreak clinical isolate strain of Salmonella enterica Newport was utilized in simulating contaminated agricultural water exposed to hypochlorite and PAA treatment. Treatments consisted of two samples, each repeated in duplicate of 10 and 20 ppm hypochlorite and PAA each, with an aqueous control. Following exposure, cells were isolated for RNA extraction and sequencing to analyze mRNA for relative differential gene expression levels. The dynamic range of cellular adaptive response to chemical stressors was seen in the overall number of differentially expressed genes. They numbered from 11 genes to 316, 1,719, and 2,010 genes respectively for 10 ppm hypochlorite, 20 ppm hypochlorite, 10 ppm PAA, and 20 ppm PAA treatments, respectively. These transcripts ranged in cellular function from biosynthesis to degradation, energy generation, and non-metabolically linked functions. Notably, exposure to oxidative antimicrobials resulted in genes associated with key virulence, attachment, and gene transfer factors showing positive degrees of differential expression. These findings stress the importance of monitoring disinfectant application, and the potential for increasing the efficacy of treatments through further elucidation of microbial adaptive response.