Transcriptional profiling of Salmonella enterica serovar Enteritidis exposed to ethanolic extract of organic cranberry pomace

Citation

Das, Q., Lepp, D., Yin, X., Ross, K., McCallum, J.L., Warriner, K., Marcone, M.F., Diarra, M.S. (2019). Transcriptional profiling of Salmonella enterica serovar Enteritidis exposed to ethanolic extract of organic cranberry pomace, 14(7), http://dx.doi.org/10.1371/journal.pone.0219163

Plain language summary

Salmonella enterica serovars Typhimurium, Enteritidis and Heidelberg are important causes of foodborne poisoning (salmonellosis) outbreaks in human worldwide. The control of these Salmonella is difficult, because of their ability to grow and survive in the food production chain and the emergence of antimicrobial resistant (AMR) isolates. Cranberry fruits content several antimicrobial compounds that could be developed for application to improve the food safety. The present study evaluated the ability of extracts (KCOH) from organic cranberry fruit wastes (pomace) to affect Salmonella enterica serovars Typhimurium, Enteritidis and Heidelberg isolated from broiler chicken. Exposure to KCOH or its sub-fractions significantly affected the growth of these AMR Salmonella. Sub-lethal concentrations of KCOH affected mechanisms of uptake and assimilation of essential nutrients such minerals and carbohydrates in Salmonella Enteritidis which is the most common serovars from poultry implicated in human salmonellosis in Canada. Our Data showed that KCOH negatively impacted the survival of Salmonella and its ability to cause diseases. This study provided information on the response of Salmonella exposed to cranberry fruit by-products, which could be useful in developing control strategies of this important foodborne pathogen.

Abstract

Non-typhoidal Salmonella enterica serovars continue to be an important food safety issue worldwide. Cranberry (Vaccinium macrocarpon Ait) fruits possess antimicrobial properties due to their various acids and phenolic compounds; however, the underlying mechanism of actions is poorly understood. We evaluated the effects of cranberry extracts on the growth rate of Salmonella enterica serovars Typhimurium, Enteritidis and Heidelberg and on the transcriptomic profile of Salmonella Enteritidis to gain insight into phenotypic and transcriptional changes induced by cranberry extracts on this pathogen. An ethanolic extract from cranberry pomaces (KCOH) and two of its sub-fractions, anthocyanins (CRFa20) and non-anthocyanin polyphenols (CRFp85), were used. The minimum inhibitory (MICs) and bactericidal (MBCs) concentrations of these fractions against tested pathogens were obtained using the broth micro-dilution method according to the Clinical Laboratory Standard Institute’s guidelines. Transcriptional profiles of S. Enteritidis grown in cation-adjusted Mueller-Hinton broth supplemented with or without 2 or 4 mg/ml of KCOH were compared by RNA-Seq to reveal gene modulations serving as markers for biological activity. The MIC and MBC values of KCOH were 8 and 16 mg/mL, respectively, against all tested S. enterica isolates. The MIC value was 4 mg/mL for both CRFa20 and CRFp85 sub-fractions, and a reduced MBC value was obtained for CRFp85 (4 mg/ml). Treatment of S. Enteritidis with KCOH revealed a concentration-dependent transcriptional signature. Compared to the control, 2 mg/ml of KCOH exposure resulted in 89 differentially expressed genes (DEGs), of which 53 and 36 were downregulated and upregulated, respectively. The upregulated genes included those involved in citrate metabolism, enterobactin synthesis and transport, and virulence. Exposure to 4 mg/ml KCOH led to the modulated expression of 376 genes, of which 233 were downregulated and 143 upregulated, which is 4.2 times more DEGs than from exposure to 2 mg/ml KCOH. The downregulated genes were related to flagellar motility, Salmonella Pathogenicity Island-1 (SPI-1), cell wall/membrane biogenesis, and transcription. Moreover, genes involved in energy production and conversion, carbohydrate transport and metabolism, and coenzyme transport and metabolism were upregulated during exposure to 4 mg/ml KCOH. Overall, 57 genes were differentially expressed (48 downregulated and 9 upregulated) in response to both concentrations. Both concentrations of KCOH downregulated expression of hilA, which is a major SPI-1 transcriptional regulator. This study provides information on the response of Salmonella exposed to cranberry extracts, which could be used in the control of this important foodborne pathogen.