Salmonella Adhesion, Invasion and Cellular Immune Responses Are Differentially Affected by Iron Concentrations in a Combined In Vitro Gut Fermentation-Cell Model

Abstract

In regions with a high infectious disease burden, concerns have been raised about the safety of iron supplementation because higher iron concentrations in the gut lumen may increase risk of enteropathogen infection. The aim of this study was to investigate interactions of the enteropathogen Salmonella enterica ssp. enterica Typhimurium with intestinal cells under different iron concentrations encountered in the gut lumen during iron deficiency and supplementation using an in vitro colonic fermentation system inoculated with immobilized child gut microbiota combined with Caco-2/HT29-MTX co-culture monolayers. Colonic fermentation effluents obtained during normal, low (chelation by 2,2'-dipyridyl) and high iron (26.5 mg iron/L) fermentation conditions containing Salmonella or pure Salmonella cultures with similar iron conditions were applied to cellular monolayers. Salmonella adhesion and invasion capacity, cellular integrity and immune response were assessed. Under high iron conditions in pure culture, Salmonella adhesion was 8-fold increased compared to normal iron conditions while invasion was not affected leading to decreased invasion efficiency (−86%). Moreover, cellular cytokines IL-1β, IL-6, IL-8 and TNF-α secretion as well as NF-κB activation in THP-1 cells were attenuated under high iron conditions. Low iron conditions in pure culture increased Salmonella invasion correlating with an increase in IL-8 release. In fermentation effluents, Salmonella adhesion was 12-fold and invasion was 428-fold reduced compared to pure culture. Salmonella in high iron fermentation effluents had decreased invasion efficiency (−77.1%) and cellular TNF-α release compared to normal iron effluent. The presence of commensal microbiota and bacterial metabolites in fermentation effluents reduced adhesion and invasion of Salmonella compared to pure culture highlighting the importance of the gut microbiota as a barrier during pathogen invasion. High iron concentrations as encountered in the gut lumen during iron supplementation attenuated Salmonella invasion efficiency and cellular immune response suggesting that high iron concentrations alone may not lead to an increased Salmonella invasion.

Nutritional iron turned inside out: intestinal stress from a gut microbial perspective

“…We found that adhesion of several enteric pathogens to intestinal epithelial cells was markedly increased by iron in vitro (Kortman et al ., ). A recent study confirmed this effect, but also showed that iron‐induced adhesion was minimised when S. Typhimurium was in an environment with bacterial metabolites, originating from an in vitro fermentation model (Dostal et al ., ). Other factors such as iron availability in the different media (cell culture medium vs. fermentation medium) or the deteriorating effect of fermentation medium on cultured intestinal epithelial cells may, however, have contributed to those findings.…”

Non-animal models of epithelial barriers (skin, intestine and lung) in research, industrial applications and regulatory toxicology

“…Currently, a clear limitation in studying human pathogens is the availability of relevant humanized infection models. This is particularly true for obligate human pathogens (e.g., Salmonella, Helicobacter pylori and Campylobacter jejuni) for which no animal reservoir is known (Dostal et al, 2014;Höner zu Bentrup et al, 2006;Naughton et al, 2013). Since simple cell culture systems and also animals are highly artificial models for obligate human pathogens, novel human infection models based on engineered human tissue are needed and are in fact currently under development (unpublished data).…”

Human Genome-Wide RNAi Screen for Host Factors That Facilitate Salmonella Invasion Reveals a Role for Potassium Secretion in Promoting Internalization

“…In addition to genes involved in potassium transport, the molecular function categories of metal ion binding and transport were also highly enriched with p-values of 7.15 X 10 −8 and 6.49 X 10 −7 respectively. Iron has been shown to play a role in regulating invasion[20]. …”