Identification and Characterisation of an Iron-Responsive Candidate Probiotic

Abstract

BackgroundIron is an essential cofactor in almost all biological systems. The lactic acid bacteria (LAB), frequently employed as probiotics, are unusual in having little or no requirement for iron. Iron in the human body is sequestered by transferrins and lactoferrin, limiting bacterial growth. An increase in the availability of iron in the intestine by bleeding, surgery, or under stress leads to an increase in the growth and virulence of many pathogens. Under these high iron conditions, LAB are rapidly out-competed; for the levels of probiotic bacteria to be maintained under high iron conditions they must be able to respond by increasing growth rate to compete with the normal flora. Despite this, iron-responsive genera are poorly characterised as probiotics.Methodology/Principal FindingsHere, we show that a panel of probiotics are not able to respond to increased iron availability, and identify an isolate of Streptococcus thermophilus that can increase growth rate in response to increased iron availability. The isolate of S. thermophilus selected was able to reduce epithelial cell death as well as NF-κB signalling and IL-8 production triggered by pathogens. It was capable of crossing an epithelial cell barrier in conjunction with E. coli and downregulating Th1 and Th17 responses in primary human intestinal leukocytes.Conclusions/SignificanceWe propose that an inability to compete with potential pathogens under conditions of high iron availability such as stress and trauma may contribute to the lack of efficacy of many LAB-based probiotics in treating disease. Therefore, we offer an alternative paradigm which considers that probiotics should be able to be competitive during periods of intestinal bleeding, trauma or stress.

Streptococcus thermophilus NCIMB 41856 ameliorates signs of colitis in an animal model of inflammatory bowel disease

“…Additionally, increased leaks which occur as a result of epithelial cell apoptosis have been observed in Crohn's disease and ulcerative colitis (Heller et al, 2005;Zeissig et al, 2007). We have previously shown that S. thermophilus prevents occludin degradation and breakdown of tight cell junctions induced by E. coli in vitro as well as reducing epithelial cell death (Bailey et al, 2011). In the data presented here, we have shown that S. thermophilus prevents bacterial translocation from the lumen of the gut into the intestinal tissue in colitic animals ( Figure 4).…”

“…Competition both for limited nutrients and physical attachment sites could assist in the elimination of pathogens and opportunistic pathogens. We have previously shown that, unlike the majority of conventional probiotics, S. thermophilus NCIMB 41856 can compete with the resident microflora for iron, abundant in the IBD gut and used by many bacterial strains as a growth factor (Bailey et al, 2011). In the data presented here, we have shown that, in addition to this, it can compete for physical attachment sites at the iron-rich intestinal mucosa and therefore occupy a niche which could otherwise be inhabited by potentially pathogenic bacterial species.…”

“…However, given the reduction in bacterial translocation seen in this colitis model following S. thermophilus treatment, it seems likely that these IELs are of a protective rather than a colitogenic phenotype. Since we have previously shown that S. thermophilus is able to maintain tight cell junctions in vitro in the absence of IELs (Bailey et al, 2011), we hypothesise that it exerts two different mechanisms to enhance mucosal barrier integrity: preservation of occludin expression and increasing numbers of IELs which are multifunctional in maintaining a competent epithelial barrier.…”

“…We previously identified an isolate of Streptococcus thermophilus (NCIMB 41856) with the ability to reduce epithelial cell death, maintain tight cell junctions, reduce pathogen binding to epithelial cells, and reduce pro-inflammatory signalling from epithelial cells and intestinal leukocytes in vitro (Bailey et al, 2011). This strain is unusual amongst lactic acid bacteria as it has the ability to increase its growth rate in response to iron (Bailey et al, 2011).…”

“…This strain is unusual amongst lactic acid bacteria as it has the ability to increase its growth rate in response to iron (Bailey et al, 2011). While iron is not required for S. thermophilus NCIMB 41856 to exert its beneficial effect, the ability to use it as a growth factor better equips it to compete with the resident flora and pathogens in the iron-rich environment of the IBD gut.…”