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 RNASeq 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.
Highlights
Despite control measures and efforts deployed in food production continuum, non-typhoidal Salmonella enterica serovars continue to rank among the most common causes of bacterial gastroenteritis worldwide [1, 2]
The two major sub-fractions of interest enriched for anthocyanins (CRFa20) and flavonols (CRFp85) prepared from KCOH were analyzed by UPLC-MS
We have examined the antibacterial activities of KCOH and two of its sub-fractions (CRFa20 and CRFp85) against different serovars of Salmonella and explored its effects on the transcriptional profile of S
Summary
Despite control measures and efforts deployed in food production continuum, non-typhoidal Salmonella enterica serovars continue to rank among the most common causes of bacterial gastroenteritis worldwide [1, 2]. Heidelberg were among the top Salmonella serovars involved in human salmonellosis in 2017 [5]. In the last 10 years, the incidence of Salmonella Enteritidis (SE) has increased three-fold in Canada, and a similar increase of this serovar isolate from poultry sources has been documented nationally during the same timeframe [2]. Salmonella enterica serovars asymptomatically colonize the alimentary tracts of poultry. Among the non-typhoidal Salmonella, SE is the most invasive associated with poultry reproductive tissues. In Canada, the overall proportion of SE identified among retail chicken breast samples increased significantly from 8% in 2015 to 17% in 2016 [5]
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