Selenium reduces enterohemorrhagic Escherichia coli O157:H7 verotoxin production and globotriaosylceramide receptor expression on host cells.

AIM: This study investigated the efficacy of selenium (Se) in reducing Escherichia coli O157:H7 verotoxin production and toxin gene expression. Additionally, the effect of Se on globotriaosylceramide (Gb3) receptor in human lymphoma cells was determined. MATERIALS & METHODS: The effect of Se on verotoxin synthesis was determined by standard ELISA, whereas its effect on Gb3 receptor was determined by flow cytometry and real-time quantitative PCR. RESULTS & CONCLUSIONS: Se reduced extracellular and intracellular verotoxin concentration by 40-60% and 80-90%, respectively (p < 0.05), and downregulated verotoxin genes (p < 0.05). Se reduced Gb3 receptor synthesis in lymphoma cells, and real-time quantitative PCR data revealed a significant downregulation of LacCer synthase gene (GalT2) involved in Gb3 synthesis. Further studies are warranted to validate these results in an appropriate animal model.

Plant-derived antimicrobials reduce E. coli O157:H7 virulence factors critical for colonization in cattle gastrointestinal tract in vitro.

This study investigated the effect of subinhibitory concentrations (SIC) of five plant-derived antimicrobials (PDAs), namely, trans cinnamaldehyde, eugenol, carvacrol, thymol, and ß-resorcylic acid, on E. coli O157:H7 (EHEC) attachment and invasion of cultured bovine colonic (CO) and rectoanal junction (RAJ) epithelial cells. In addition, PDAs' effect on EHEC genes critical for colonization of cattle gastrointestinal tract (CGIT) was determined in bovine rumen fluid (RF) and intestinal contents (BICs). Primary bovine CO and RAJ epithelial cells were established and were separately inoculated with three EHEC strains with or without (control) SIC of each PDA. Following incubation, EHEC that attached and invaded the cells were determined. Furthermore, the expression of EHEC genes critical for colonization in cattle was investigated using real-time, quantitative polymerase chain reaction in RF and BICs. All the PDAs decreased EHEC invasion of CO and RAJ epithelial cells (P < 0.05). The PDAs also downregulated (P < 0.05) the expression of EHEC genes critical for colonization in CGIT. Results suggest that the PDAs could potentially be used to control EHEC colonization in cattle; however follow-up in vivo studies in cattle are warranted.

Inactivation of Listeria monocytogenes on frankfurters by plant-derived antimicrobials alone or in combination with hydrogen peroxide.

Listeria monocytogenes is a significant foodborne pathogen associated with outbreaks involving contaminated ready-to-eat (RTE) products, including frankfurters. The USDA-FSIS has established a zero tolerance policy for L. monocytogenes in RTE products, thereby warranting effective post-processing interventions to control the pathogen on these foods. In the present study, the antilisterial activity of GRAS (generally recognized as safe)-status plant-derived antimicrobials (PDAs), namely ß-resorcylic acid (BR), carvacrol (CR), and trans-cinnamaldehyde (TC) either alone or in combination with hydrogen peroxide (HP) as post-processing dip treatments on frankfurters was investigated. Frankfurters were surface inoculated with a five-strain mixture of L. monocytogenes (~6.0 log CFU per frankfurter), followed by dip treatment at 55 °C for 60s or 65 °C for 30s in sterile deionized water, or water containing BR (1.5%), CR (0.75%), or TC (0.75%) either alone or in combination with HP (0.1%). Treated frankfurters were vacuum-packaged, and stored at 4 °C for 70 days. Representative samples were analyzed on days 0, 1, 3, 7, 14, 28, 42, 56, and 70 of refrigerated storage for enumerating surviving L. monocytogenes on frankfurters. Six frankfurters were sampled at each time point for each treatment. On day zero, all PDAs reduced L. monocytogenes counts by >2 log CFU/frankfurter at both temperatures (P<0.05), compared to controls. From days 1 to 70, L. monocytogenes counts on PDA-treated frankfurters were consistently lower (P<0.05) and after 70 days of storage, the pathogen counts were reduced to undetectable levels on frankfurters treated with PDA-HP combinations at 65 °C, and by combinations of BR and TC with HP at 55 °C. Results suggest that PDAs alone, or in combination with HP could be effectively used as post-processing dips to reduce L. monocytogenes on frankfurters, although follow-up studies on sensory and quality characteristics of PDA-treated frankfurters are necessary.

Plant-derived antimicrobials reduce Listeria monocytogenes virulence factors in vitro, and down-regulate expression of virulence genes.

Listeria monocytogenes (LM) is a major foodborne pathogen causing septicemia, meningitis and death in humans. LM infection is preceded by its attachment to and invasion of human intestinal epithelium followed by systemic spread. The major virulence factors in LM include motility, hemolysin and lecithinase production. Reducing LM attachment to and invasion of host tissue and production of virulence factors could potentially control listeriosis in humans. This study investigated the efficacy of sub-inhibitory concentrations (SICs, concentrations not inhibiting bacterial growth) of three, generally regarded as safe (GRAS)-status, plant-derived antimicrobial compounds in reducing LM attachment to and invasion of human colon adenocarcinoma (Caco-2) and human brain microvascular endothelial cells (HBMEC). Additionally, the effect of these compounds on the aforementioned LM virulence factors was studied. The compounds and their respective SICs used relative to their MICs were trans-cinnamaldehyde (TC 0.50mM, 0.75mM with the MIC of 0.90mM), carvacrol (CR 0.50mM, 0.65mM with the MIC of 0.75mM), and thymol (TY 0.33mM, 0.50mM with the MIC of 0.60mM). All three-plant antimicrobials reduced LM adhesion to and invasion of Caco-2 and HBMEC (p<0.05). The compounds also decreased LM motility, hemolysin production and lecithinase activity (p<0.05). Real-time PCR data revealed that TC, CR, and TY down-regulated the expression of LM virulence genes by >3.0 folds compared to controls (p<0.05). Results suggest that TC, CR, and TY could potentially be used to control LM infection; however, in vivo studies are necessary to validate these results.