本帖最后由 悟空の格古洛 于 2016-8-4 02:16 编辑 如题。
话说我这帖子之所以标“灌水”而不标“求助”就是因为我其实实在也不指望你们………
总之英文我贴在下面了，有吃饱了撑的闲的没事干的就帮我看看吧…………= =|||||||||||
Where Do Probiotic Bacteria Come From?
Selection of strains for probiotic use should always follow two general principles:safety of the organism,and possessing desirable characteristics for its intended use.Intestinal probiotics are dominated by members of Bifidobacterium and Lactobacillus,as these two genera have a long history of safe use and have GRAS(generally regarded as safe)status.They are also very suited to augmenting the intestine,，as Bifidobacterium,is a major inhabitant of the large intestine and Lactobacillus is a major inhabitant of the small intestine.The origin of the strains used in probiotics can be either freshly isolated from a human or animal host or from a culture collection Culture collection strains have generally been extensively cultivated in fermentation systems and thus have likely attenuated to suit the in vitro environment.However,as stated by Havenaar et al(18),the choice of where to get a probiotic strain depends on the specific purpose of the probiotic. For example,if only transient activity of the probiotic is needed,such as for lactose digestion,the it is not necessary for the probiotic to have characteristics that would enable it to colonize the host.Most probiotic effects in the GI system would be enhanced if the probiotic would be able to compete with the indigenous flora.This requires a more careful selection of strains.Although all the criteria for this purpose are not currently known for any intestinal organism,there is one general consensus pertaining to a criterion that is important.That consensus is that the probiotic should originate from the same animal species that it is intended to target (19,20).The rationale is that the intestinal environments in different animal species are sufficiently different such that the most competitive bacteria in each host species have evolved specific traits for survival in that host(21).Human probiotics,Therefore,should originate from a human source if the objective is to effectively modulate the microbial populations at their target sites.
It is noteworthy that when commercial probiotics are fed to human subjects during controlled feeding studies,the probiotic can be detected in high numbers in the feces during the feeding period,but rapidly disappears following cessation of feeding(22).The rate of decrease of the probiotic following feeding is generally less than 1 week(figure4.2).Some probiotics such as Lactobacillus rhamnosus GG can in some cases persist longer than a week postfeeding(23).The lack of detection of the probiotic postfeeding indicates that it is not able to compete very well with the endogenous strains of that species.This is to be expected because the endogenous strains are adapted to their environment,whereas the probiotic strain may not have all the traits necessary to compete with it.Unfortunately,all of the necessary traits are not yet known,but significant progress has been made,and this is discussed in a following section.
Species Used as Probiotic Cultures
Probiotics for human probiotics are dominated by different species and strains of the genera Lactobacillus and Bifidobacterium(Table 4.1).A primary reason for this in that both these genera are dominant inhabitants of their respective niches in the large intestine,Lactobacillus in the small intestine and Bifidobacterium in the large intestine.Of the lactobacilli.L.acidophilus is by far the most widely used probiotic as it has a long history of research and use.Many of the other Lactobacillus species listed in Table 4.1 are closely related to L.acidophilus.This long history dates back to the early 1900s when significant research on intestinal flora followed Metchnikoff 's work with a lactic acid-producing bacterium,then called Bacillus bulgaricus,found in a yogurt product.AS L.acidophilus is a related bacterium and one of the predominant organisms in the intestinal tract of breast-fed babies,it quickly took the place of L.bulgaricus as the probiotic of choice in the U.S.(24).It,therefore,has almost 100 years of use in human diets.Another very popular Lactobacillus probiotic is L.casei,as it is thought to significantly enhance the immune system by inducing IL-12 and IFNr expression and activates NK cell tumoricidal activity,as well as stimulating the production of secretory IgA(25.26).This has been the foundation for the successful probiotic beverages shown in Figure 4.1.It is thought the high immune response is because they colonize the small intestine in the vicinity of the Peyer 's patches,which are very immunogenic.Many other lactobacilli,as sell as some bifidobacteria,also have been shown to stimulate an enhanced immune response(25).
582 ↙ ↙
发表于 2008-6-18 17:52
楼主
发表于 2008-6-18 19:40
发表于 2008-6-18 21:18
