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Probiotics gain more interest

With the current regulatory issues associated with antibiotic growth promoters, the number of studies examining alternatives is increasing. Two areas that are receiving a great deal of interest are probiotics and functional carbohydrates.

While most people are aware of probiotics, functional carbohydrates may be a new term to many. The continuous administration of beneficial bacteria (probiotics),

specific substrates for beneficial bacteria (fermentable prebiotics) and functional carbohydrates (such as MOS, which is capable of eliminating potential bacteria), ensure that a stable intestinal microflora (eubiosis) is maintained.

Problems in the past with probiotics may revolve around poor product quality or misrepresented product with low or no viable organisms. In addition, pelleting temperatures and preservatives applied to feed may adversely affect probiotic preparations. Despite an inconsistent track record in the past, the probiotics of today are more stable and of better quality than ever before.

Effect of probiotics

The benefits of lactic acid bacteria as probiotics include the establishment or restoration of a healthy GI tract (Szajewska et al., 2006), reduced fecal odour, acidification of the GI tract, metabolites that may inhibit pathogens (Newman, 1990), improved immune function (Sekine et al., 1995) and anti-carcinogenic properties. There are a number of metabolites that have been reported to be inhibitory to a number of pathogenic bacteria. These metabolites include organic acids, peroxides, bacteriocins and broad-spectrum antimicrobial compounds. Trials in rodents have demonstrated that rats supplemented with viable cultures of L. acidophilus had lower concentrations of nitroreductase a suspected carcinogen (Goldin and Gorbach, 1977). Similar data also exist using Bifidobacteria as a supplement with the relative rate of azoxymethane-induced aberrant crypt formation reduced in rats receiving the Bifidobacteria (Kulkarni and Reddy, 1994). In vivo studies in boars have shown that animals receiving L. acidophilus yogurt had reduced concentrations of fecal coliforms compared to unsupplemented boars (Danielson, et al., 1989). Additional studies have also examined coliform concentrations throughout the GI tract and found similar responses. However, studies have also found no effect associated with probiotic products in broilers (O'Dea et al ., 2006).

Bacillus strains

Bacillus strains of bacteria have also been used as probiotics (also with mixed results). One of the most attractive aspects of Bacillus species is the ability of these organisms to form temperature resistant and stable spores. Spore-forming bacteria can tolerate higher temperatures and pressures and thus remain viable. One potential problem with the use of Bacilli may be whether these organisms can revert to the vegetative state in the gastrointestinal tract of the animal (Newman and Jacques, 1995). In a study using dogs, examination of the fecal bacterial population demonstrated that both vegetative and sporulated forms of Bacillus were present, indicating that the particular strain used in this trial could, in fact, germinate in the GI tract (Biourge et al., 1998). Trials in other species have demonstrated reductions in mortality with Bacillus subtilis supplemen tation (Pollman et al ., 1984). This may be due to the antigenic properties of the cell wall and capsule of the Bacillus, eliciting an immune reaction. Other investigations have demonstrated immune responses to viable microorganisms and/or their cellular components. One limitation in a review of probiotic effects is that bacteria are heterogeneous in nature and the diversity of genera, species and strains make it difficult to deduce general conclusions about probiotics as a whole. When considering probiotics it is prudent to consider the data on the specific product.

Functional carbohydrates

Modulating the microbial community in the gastrointestinal tract through food or feed ingredients (prebiotics), can influence and preserve health. This is due to the stimulation of beneficial microorganisms; however, these ingredients may also attenuate the virulence of pathogens, as well as enhance the anti-adhesive effect against pathogenic bacteria (Steer, et al., 2000). The first line of defence against pathogens in the digestive tract is the oligosaccharide receptors. Pathogen receptors have strict requirements for their ligands (proteins and glycoproteins) and often consist of a combination of monosaccharides (Steer, et al., 2000). Many gram-negative bacteria have surface organelles known as type 1 fimbriae, which mediate D-mannose-sensitive binding. When mannose is added to the diet of young chicks, the colonisation of S. typhimurium is reduced. However, the binding strength can vary depending of the receptor composition (Bar-Shavit et al., 1979; Salit and Gotschlich, 1977). D-mannose, yeast mannan and alpha-methyl-D-mannoside have the ability to interfere with E. coli binding, while other common carbohydrates have little effect. In fact, mannosides (mannan oligosaccharides or MOS) have shown better inhibition when compared to D-mannose, which support the hypothesis that the receptor may be an oligosaccharide rather than a monosaccharide (Jones and Isaacson, 1983). Depending on their structure (linear or branched), the chemical or physical properties of natural oligosaccharides diverge with a or ß linkages and variations in the type of monomers present (Strickling et al., 2000). Most plant mannans have beta 1-4 linkages that are thought to have little or no ability to bind E. coli and Salmonella compared with yeast mannans which contain alpha mannan linkages. This is because of the differences in carbohydrate linkages. At the same time, the specific structure and presentation of the yeast mannan is also very important in reaping the benefits of mannan oligosaccharide products. The diversity of benefits observed from a specific MOS product include reductions in pathogens, improved gut health, immune modulation and improved animal performance (Lou et al., 1995; Pirvulescu et al., 2000; Yun-Lan et al., 2004; Finucane et al., 1999; Spring et al., 2000; Franklin et al., 2005; Franklin et al., 2002; Newman

and Newman, 2001; O'Quinn, et al., 2001; Hooge, 2002; Hooge, 2003; Hooge, 2004; Hooge, 2006; Miguel et al ., 2004). As is the case with probiotics, the enormous diversity of oligosaccharides makes it important to consider the data that has been generated from a specific MOS product before implementing a product into a feeding programme (Table 1).

Feed the beneficial bacteria

Fructooligosaccharides (FOS) have also been examined for pathogen inhibition. The principle behind the use of FOS involves the structure and bonding of the fructose molecules. Purified preparations of FOS have been shown to provide a nutrient source for beneficial bacteria, such as Bifidobacteria and certain lactobacilli. It is thought that supporting the growth of the beneficial bacteria will provide an in situ competitive exclusion (CE) effect, thus improving animal health. It seems important, however, that the concentration of non-complex fructose molecules be kept to a minimum in order for this oligosaccharide to be successful. Oyarzabal and coworkers (1995) found that Salmonella ssp. could not use a purified fructooligosaccharide (FOS) preparation for growth, but were able to utilise a commercial preparation of FOS.

It is assumed that probiotics, prebiotics and functional carbohydrates ensure that a stable intestinal microflora is maintained

The authors suggest the use of lactic acid bacteria in combination with FOS as a feasible approach to control Salmonella. Other studies have demonstrated a reduction in Salmonella concentrations in birds challenged with S. typhimurium with and without FOS and a CE culture. FOS alone had little effect on Salmonella exclusion when FOS was administered after infection; however, FOS in combination with a defined CE product had an additive effect on Salmonella exclusion, especially when used as a prophylactic prior to Salmonella infection (Bailey et al ., 1991). Waldroup and coworkers (1993) found that supplementing broilers with 0.375% FOS had few consistent effects on production parameters or carcass Salmonella concentrations. These authors also caution of possible antagonism between FOS and BMD. Human data for FOS is much more consistent. Hidaka et al. (1986) found that consumption of 8-g/day FOS increased numbers of bifidobacteria, improved blood lipid profiles and suppressed putrefactive substances in the intestine.

However, a concern with prebiotics that are fermented in the GI tract (Inulin and FOS) is a concomitant production of excess gas, resulting in flatulence, bloating and abdominal discomfort (Grizard and Barthoeuf, 1999).

Conclusions

While there is still much work to be carried out to demonstrate the probiotic effect in all species, there is a growing recognition that non-digestible oligosaccharides are more than an energy source for the hindgut microflora. They also play a vital role in cellular metabolism, protein structure and function, cell-to-cell communication and host immunity. In animals, the dietary inclusion of prebiotics has been demonstrated to have a broad range of physiological responses through modification in gastrointestinal tract activity, which can influence physiological activity elsewhere in the body, such as energy and lipid metabolism, endocrine function and immune status. These functional carbohydrates, with cost of production, simple extraction technology and potential infinite supply, will dominate the growth promoter market for the foreseeable future.

References are available on request .

Dr Kyle Newman received his bachelor of science in physiology and Zoology from the University of Wyoming, USA. He went on to complete his masters in microbiology, specialising in microbial physiology and the biochemistry of microbial growth. He received his Phd from the University of Kentucky, specialising in nutritional microbiology. Before joining venture laboratories as the laboratory director, Dr Newman served as director of laboratories at Alltech, inc. he currently heads a team of scientists with research projects in the food and agriculture industries and consultation on HACCP, feed and food safety.

Source: Feed Mix magazine Volume 15 nr.1

Editor AllAboutFeed

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