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PREBIOTICS and various studies
« Thread started on: Sep 12th, 2006, 09:15am »
Maintaining gut health in meat-type poultry without antibacterial growth promoters and ionophores
SUMMARY> Potential alternatives to in-feed antibiotics (antibacterial growth promoters and ionophorous anticoccidials) as preventive measures against intestinal health problems in poultry are reviewed. The focus is on Clostridium perfringens-associated disease, which is expected to become one of the most important negative consequences if all use of in feed antibiotics is abolished. While anticoccidial vaccines are available and likely to exert satisfactory preventive effect against intestinal coccidia, no satisfactory non-antibiotic measures against C.perfringens have been identified. Anticlostridial vaccination may become an option in the near future, but whether such vaccination can fully replace in-feed antibiotics remains to be seen. Use of undefined bacterial cultures has shown promising results, but more work is desirable to establish optimal methods for preparation and practical use of such products specifically against C.perfringens.
The issue of non-antibiotic prevention of C.perfringens-associated problems is seriously under-researched.
Enteric bacterial infections and in-feed antibotics
Campylobacter jejuni (Sahin et al., 2002) and most types of Salmonella infections (Thorns, 2000) primarily imply a health risk to consumers of poultry. Other bacteria cause concern because they induce intestinal disease in the birds. Among the most gut-specific pathogens (Porter, 1998), C. perfringens is assumed to represent the main health problem associated with an abolished use of in-feed antibiotics. Campylobacter jejuni and Salmonella enterica are less likely to become an increased problem as consequence of this development. In fact experimental evidence suggests that such additives may promote an enteric Salmonella infection in chickens (Holmberg et al., 1984; Manning et al., 1994). The group of bacteria causing impaired production performance is less well defined than the zoonotic and bird-pathogenic
organisms. The fact that most AGPs target Gram positive bacteria suggests that this group of bacteria is an important cause of impaired performance. Many mechanisms are assumed to be involved in this effect of the gut flora (Bedford, 2000). A mechanism that has been studied recently, is bacterial deconjugation of bile salts rendering free bile salts with lower detergent properties in the emulsification of fat. This process has been associated with impaired fat digestion and growth depression in broilers (Knarreborg, 2002). Oral treatments, and additives to feed or drinking water UNDEFINED MICROBIAL CULTURES In newly hatched chicks, the rapid establishment of an adult-type intestinal microflora, via the oral route, produces almost immediate resistance to colonisation by salmonellas that gain access to the rearing environment (Mead, 2000). Products based on this ‘competitive exclusion’ (CE) principle are categorised by the World Health Organization (1994) as ‘normal gut flora’ products, and described as ‘an undefined preparation of live obligate and facultatively anaerobic bacteria, originating from normal, healthy individuals of an avian species, which is free from specific pathogenic microorganisms and is quality controlled.’ The efficacy of CE products probably depends on their complexity and the fact that they include important elements of the normal microflora. Studies have revealed that preparations conferring protection against salmonellas can be ineffective againstCampylobacter jejuni colonization (Mead, 2002), which suggests that different members of the bacterial flora may exert a protective role against different pathogens. Variations in how CE materials are prepared may be important, possibly because different types of bacteria require different handling in order to maintain their protective capability. Reduced levels of caecal C.perfringens by use of CE was noted by Barnes et al. (1980) and Snoeyenbos et al. (1983). Further, Elwinger et al. (1992) in a pen trial found that the use of a commercial CE product was associated with reduced incidence of necrotic enteritis and reduced caecal carriage of C.perfringens in broiler chickens. Hofacre et al. (1998) challenged broiler chickens experimentally with C.perfringens, and found that normal gut flora products reduced gross intestinal lesions and improved feed efficiency in their disease model. Also, a CE product reduced C.perfringens counts and the percentage of C.perfringens positive broilers reared on wire floor and offered a rye-supplemented feed (Craven et al., 1999).
Finally, in a field study, CE treatment was associated with delayed intestinal proliferation of C.perfringens, delayed appearance of C.perfringens-associated gut lesions and improved production performance at slaughter (Kaldhusdal et al., 2001). These results suggest that CE treatment may contribute to a successful replacement of in-feed antibiotics. Commercial CE products are available (Mead, 2000), but more work would be useful in order to establish optimal methods for preparation and practical use of CE products specifically intended for use against C.perfringens.
DEFINED MICROBIAL CULTURES OR PRODUCTS (‘PROBIOTICS’) The term ‘probiotic’ has been defined as ‘mono- or mixed cultures of living microorganisms, which beneficially affect the host by improving the properties of the indigenous microflora’ (Ghadban, 2002). Some workers have also included killed bacterial
cultures and bacterial metabolites in their definition of probiotics (Reuter, 2001). The definition of probiotics does not exclude CE products, and these undefined cultures are sometimes considered an integral part of the probiotics concept. However, the term ‘probiotic’ is often restricted to products containing cells or
metabolites from defined strains of microorganisms, and commercial products usually are based on one or a few bacterial or fungal species. Much work has been done to establish defined bacterial cultures that are equally effective as undefined cultures againstsalmonella colonisation in...
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The following article-study is posted FYI
Fermentation of fructooligosaccharides (FOS) and other oligosaccharides has been suggested to be an important property for the selection of bacterial strains used as probiotics. However, little information is available on FOS transport and metabolism by lactic acid bacteria and other probiotic bacteria. The objectives of this research were to identify and characterize the FOS transport system of Lactobacillus paracasei 1195. Radiolabeled FOS was synthesized enzymatically from [3H]sucrose and purified by column and thin-layer chromatography, yielding three main products: glucose (G) á-1,2 linked to two, three, or four fructose (F) units (GF2, GF3, and GF4, respectively). FOS hydrolysis activity was detected only in cell extracts prepared from FOS- or sucrose-grown cells and was absent in cell supernatants, indicating that transport must precede hydrolysis. FOS transport assays revealed that the uptake of GF2 and GF3 was rapid, whereas little GF4 uptake occurred. Competition experiments showed that glucose, fructose, and sucrose reduced FOS uptake but that other mono-, di-, and trisaccharides were less inhibitory. When cells were treated with sodium fluoride, iodoacetic acid, or other metabolic inhibitors, FOS transport rates were reduced by up to 60%; however, ionophores that abolished the proton motive force only slightly decreased FOS transport. In contrast, uptake was inhibited by ortho-vanadate, an inhibitor of ATP-binding cassette transport systems. De-energized cells had low intracellular ATP concentrations and had a reduced capacity to accumulate FOS. These results suggest that FOS transport in L. paracasei 1195 is mediated by an ATP-dependent transport system having specificity for a narrow range of substrates.
MATERIALS AND METHODS
The ability of specific dietary substances to influence the gastrointestinal microflora by increasing the population of beneficial bacteria has attracted considerable research attention. These so-called prebiotic substances are defined as food ingredients that are neither hydrolyzed nor adsorbed in the stomach or gastrointestinal tract but rather confer beneficial effects on the host by selectively stimulating the growth of desirable bacteria in the colon (14). Some investigators have suggested that the prebiotic hypothesis, if true, could be “one of the most important stories to emerge in nutrition and gut microbiology since the turn of the century” (24).
Among the prebiotic substances that have been studied, the most heavily researched are the disaccharide lactulose; the oligosaccharides, especially fructooligosaccharides (FOS) and galactooligosaccharides; and various polysaccharides, including inulin and various starch-based materials (2, 8, 9, 14, 21, 33, 41). By definition, these substances are resistant to hydrolytic enzymes and are ordinarily fermented by a narrow range of colonic bacteria (9, 14, 29). Importantly, among the bacteria that metabolize prebiotic oligosaccharides are strains of Lactobacillus and Bifidobacterium spp., organisms that are generally considered to be desirable members of the colonic microbiota (12, 19, 26). Numerous in vitro and in vivo studies have shown that these bacteria are stimulated or enriched in the presence of FOS or other oligosaccharides (3-6, 13, 17, 25, 32, 34, 39).
Recently, we screened 28 strains of lactic acid bacteria (LAB) and rela