Bacteria used in commercial probiotic preparations are most commonly gram-positive lactic acid-producing species, although there are also some probiotic products which utilise gram-negative coliform bacteria. Characterising how the innate immune system responds to these bacteria in vitro may give an indication as to the likely immunomodulatory events that can be triggered following probiotic administration in vivo. Here, an established gram-positive probiotic (Lactobacillus casei Shirota) was compared against a novel gram-negative probiotic strain (Escherichia coli Nissle 1917) for its ability to induce cytokine production in a cell type representative of the innate immune system; in addition, responses were contrasted against those induced by an enteropathogenic coliform, E. coli 2282. We investigated the ability of these three bacterial strains to modulate production of interleukins-10, -12 and -18; tumour necrosis factor-alpha; interferon-alpha; and transforming growth factor-beta, via a series of in vitro culture experiments involving the murine monocyte/macrophage cell line J774A.1. All bacteria induced marked secretion of IL-12 and TNFalpha by cells, while only coliforms induced production of IL-10; there was minimal or no induction of IL-18 or TGFbeta. Activation of cells with recombinant gamma-interferon promoted increased production of IL-12, but decreased production of IL-10, in response to the co-culture of coliform bacteria, indicating differential cytokine induction depending on the activation status of the target cell. In general, live bacteria stimulated higher levels of IL-10, IL-12 and TNFalpha secretion than heat-killed preparations, while only live coliforms induced IFNalpha. These findings are discussed in relation to the likely immunomodulatory effects of gram-positive and gram-negative bacteria on the innate immune system in vivo, with particular emphasis on the marked similarity in cytokine response patterns observed between probiotic versus pathogenic coliform bacteria.

Removal and restriction of subtherapeutic antibiotics from poultry diets in many parts of the world has amplified interest in improving intestinal health and nutrient utilization. Some probiotic (direct-fed microbials) and plant-derived (phytogenic) feed additives are gaining market presence. Defined probiotic cultures have the potential to succeed, in large part because of in vitro screening and selection. However, regulatory approval delays, particularly in Europe, have stymied the commercial application of some microorganisms in poultry diets. Phytogenic feed additives have demonstrated ranges of antimicrobial activities in vitro and are building a track record of improvements in bird performance. Hesitation by nutritionists to incorporate these feed additives are due in part to 1) unfamiliarity, 2) the overselling of plausible effects by industry, 3) product inconsistency, 4) a lack of documented physiological and microbiological effects in vivo, and, in the case of probiotics, 5) a lack of documentation of persistence.

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Yeast derivatives including yeast cell wall components are promising alternatives to antibiotics with respect to the promotion of health and performance in livestock, based on their capacity to bind enteropathogenic bacteria and to beneficially modulate the immune system. However, these mode(s) of action both in vitro and in vivo are still not well understood. Furthermore, standardization and reproducibility of in vitro techniques (microbiology, cell culture assays) are critical features for the application of yeast derivatives as well as for the proof of effectiveness. Yeast cell wall products are suggested as anti-adhesive agents and are thus proposed to prevent attachment of certain intestinal bacteria by providing alternative adhesion sites to enterobacteria, which contain mannose-specific type I fimbriae such as Escherichia coli or Salmonella spp. and which is well documented. Various in vitro assay techniques have become of paramount importance for biotechnological research since they allow for determination and quantification of potential mode(s) of action. However, in vitro assays may be criticized by product end users as not accurately reflecting in vivo responses. Pro and cons of different assays and their bias will be discussed specifically regarding yeast cell wall components and adhesion of enteropathogenic bacteria. Immunomodulation is a therapeutic approach intervening in auto-regulating processes of the defense system. Yeast derivatives such as beta-glucans are proposed to interact with cells of the innate immune system by receptor recognition. Controversial data in literature and mode(s) of action are reviewed and discussed here.

The target of the present study was to quantify the capacity of different commercially available yeast derivatives to bind E. coli F4 and Salmonella Typhimurium. In addition, a correlation analysis was performed for the obtained binding numbers and the mannan-, glucan- and protein contents of the products, respectively. In a subsequent experiment, different yeast strains were fermented and treated by autolysis or French press to obtain a concentrated yeast cell wall. The capacity of yeast cell wall products to bind E. coli F4 and Salmonella Typhimurium was assessed with a quantitative microbiological microplate-based assay by measuring the optical density (OD) as the growth parameter of adhering bacteria. Total mannan and glucan were determined by HPLC using an isocratic method and a Refractive Index (RI) Detector. Total protein was determined by Total Kjeldahl Nitrogen (TKN). Statistical analyses were performed with IBM SPSS V19 using Spearman correlation and Mann Whitney U Test.Different yeast derivatives show different binding numbers, which indicate differences in product quality.Interestingly, the binding numbers for Salmonella Typhimurium are consistently higher (between one and two orders of magnitude) than for E. coli F4.We could demonstrate some statistical significant correlations between the mannan- and glucan content of different yeast derivatives and pathogen binding numbers; however, for the different yeast strains fermented under standardized laboratory conditions, no statistically significant correlations between the mannan- and glucan content and the binding numbers for E. coli and Salmonella Typhimurium were found.Interestingly, we could demonstrate that the yeast autolysis had a statistically significant difference on E. coli binding in contrast to the French press treatment. Salmonella binding was independent of these two treatments.As such, we could not give a clear statement about the binding factors involved. We propose that many more factors apart from mannan- and glucan content, such as cell wall structure, strain diversity, structural diversity, structural surroundings, and non-specific interactions play important roles in pathogen immobilization.