Salmonella infection is one of the most common food-borne illnesses in the world. Most human infections are food-borne and are caused by Salmonella Enteritidis and Salmonella Typhimurium.
Mannose- mode of action
Mannose is a monosaccharide with high binding specificity for Fim H adhesins of type I fimbriae on the surface of many Enterobacteria. Fimbriae are used by Enterobacteria to recognise mannose residues on glycoproteins of the intestinal epithelial cell surface. this is how these pathogens adhere to the intestinal wall as a previous and key step to penetrating enterocytes and invading the lymphoid tissue.
Therefore, the use of mannose rich compounds prevents the bacterial ability to invade by blocking their fimbriae. However, it is not just the contents of mannose, but also the structure of the molecule, what determines the efficacy of these carbohydrates. For this reason, simple mannose monomers have low blocking capacity on bacterial fimbriae, and the resulting levels of intestinal tissue damage are similar to those of untreated animals. On the contrary, oligomannans (small to medium sized carbohydrates containing mannose) have been shown to be very efficient and have prebiotic proroperties which promote the gut flora and the competitive exclusion of pathogens.
Salmosan is a source of vegetal β-galactomannans obtained after a technological process in which mannose long chains are fragmented by depolymerisation, neutralising thickening properties and maximising it Salmonella-blocking effect.
In Vitro Trials
The efficacy of β-galactomannans against Salmonella was studied in vitro in different studies with intestinal cell cultures. These studies showed that, in the presence of β-galactomannans at 0.5 μg/mL, the invasion of intestinal cell by Salmonella Typhimurium added to the cell culture (4*106CFU) was inhibited significantly about 60% versus the positive control (Figure 1). In the presence of β-galactomannan levels of 10 μg/mL, the reduction was above 70%.
Salmonella remains blocked and is agglutinated by the hydrolysed β-galactomannans (Figure 2). The rugged, spherical structure of the β-galactomannans is seen clearly in this image; this struture facilitates the binding of bacteria to the molecules of mannose. The bacteria blocked by β-galactomannans are excreted in the faeces and have no infective capacity.
Figure 2: Electron microscope image of β-galactomannans
agglutinating Salmonella in chicken gut tissue.
In vivo Trials
Layers
Regarding in vivo efficacy, in a trial with 225 HyLine laying hens, animals were divided into two groups, a group fed with 500 g/ton β-galactomannans, and a control group. Twenty seven days after starting the treatment, animals were challenged with 109 CFU of Salmonella enterica enterica Enteritidis (oral inoculation; 1 mL of suspension). Microbiological examination of caecum in the treated group showed that susceptibility to infection was lower than control baseline (6.3% vs. 25%). In addition, at four months post-inoculation, infected animals in the treated group no longer excreted the pathogens (Figure 3) and their tissues did not appear to be infected. This indicates that β-galactomannans at 500 g/ton are effective for the control of Salmonella in laying hens, reducing the percentage of positive animals.
Broilers
In an experiment performed with broilers, 800 1-day males were divided into five experimental groups depending on the inclusion level of β-galactomannans in feed (0%, 0.05%, 0.1%, 0.15%, 0.2%), with 16 replicates/group. All of them were doubly inoculated (two consecutive days) with 1 x 106 - 1.5 x 106 CFU of Salmonella enterica enterica Enteritidis.
It was observed that β-galactomannans reduced the isolation of Salmonella Enteritidis from caecum in a dose-dependent manner. With the higher inclusion level, the decrease in bacterial count was nearly three logarithmic units versus infected control (3.49 vs. 6.26) even just 14 days after inoculation (figure 4).
Conclusions:
β-galactomannans block Enterobacteria such as Salmonella joining to their fimbriae, preventing them from invading the intestinal mucosa.
β-galactomannans, at 500g/tonne, are effective for the control of Salmonella in laying hens, reducing the percentage of positive animals. In addition, at four months post-inoculation, infected animals in the treated group no longer excreted the pathogen and their tissues did not appear to be infected.
In broilers, β-galactomannans (2 kg/ton) reduced bacterial counts nearly three logarithmic units versus infected control (3.49 vs. 6.26) even just 14 days after inoculation.
Broilers
In an experiment performed with broilers, 800 1-day males were divided into five experimental groups depending on the inclusion level of β-galactomannans in feed (0%, 0.05%, 0.1%, 0.15%, 0.2%), with 16 replicates/group. All of them were doubly inoculated (two consecutive days) with 1 x 106 - 1.5 x 106 CFU of Salmonella enterica enterica Enteritidis.
It was observed that β-galactomannans reduced the isolation of Salmonella Enteritidis from caecum in a dose-dependent manner. With the higher inclusion level, the decrease in bacterial count was nearly three logarithmic units versus infected control (3.49 vs. 6.26) even just 14 days after inoculation (figure 4).
Conclusions:
β-galactomannans block Enterobacteria such as Salmonella joining to their fimbriae, preventing them from invading the intestinal mucosa.
β-galactomannans, at 500g/tonne, are effective for the control of Salmonella in laying hens, reducing the percentage of positive animals. In addition, at four months post-inoculation, infected animals in the treated group no longer excreted the pathogen and their tissues did not appear to be infected.
In broilers, β-galactomannans (2 kg/ton) reduced bacterial counts nearly three logarithmic units versus infected control (3.49 vs. 6.26) even just 14 days after inoculation.
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