Probiotics, unlike antibiotics, imply the use of live microorganisms rather than specific products of their metabolism. Not being specific molecules therefore, they are difficult to quantitate and even more difficult to describe in terms of proposed modes of action. Probiotics can be classified into two major types - viable microbial cultures and microbial fermentation products. Most research has centered on Lactobacilli species, Bacillus subtilis and some Streptococcus species. Similar to the situation with antibiotics, the mode of action is still unclear although the following have been suggested: a) beneficial change in gut flora with reduction in population of E. Coli; b) lactate production with subsequent change in intestinal pH; c) production of antibiotic-like substances; d) reduction of toxin release (suppression of E. coli). With these varied potential routes of activity, it is perhaps not too surprising that research results are inconsistent. In most instances, the feeding of live cultures modifies the gut microflora of birds usually with increases in number of Lactobacilli at the expense of coliforms. A healthy animal has a preponderance of lactic acid producing bacteria, and so it is only under situations of 'stress', when coliforms often increase in numbers, that probiotics will be of measurable benefit. In this context there is interest in the use of live cultures administered (orally) to day-old poultry as a means of preventing harmful bacteria such as salmonella from colonizing the gut.
The term 'competitive exclusion' is often used synonymously with probiotics. It is assumed that the probiotic will have a competitive advantage over any inherent pathogen, and either replace it, or prevent its colonization. Bacterial antagonism may arise due to synthesis of inhibitors by the probiotic organism. Lactic acid from Lactobacilli and other species is an example of such a product. Probiotic organisms may also stimulate mucosal immunity. While undefined mixtures of bacteria, usually derived from cecal contents of healthy adult birds, seem to be effective probiotics, regulatory agencies are often concerned about dosing animals with unknown organisms. Defined synthetic mixtures of bacteria seem less efficacious at this time, possibly because we have only scant knowledge of the normal (beneficial) microbial population within a healthy bird. However, this approach to developing a probiotic probably has the best long-term chance of success. With potential instability in most feeds for many Lactobacillus species, there has been recent interest in probiotics based on Bacillus subtilis species, because they possess a viable spore that has greater stability than do most lactic acid producing cultures.
Regardless of somewhat inconclusive results, it appears that probiotic use is increasing, and that the animal industry looks to such products as the substitutes for conventional antibiotics. These products seem ideal candidates for genetic manipulation which has been inferred by a number of researchers in this area. By using genetic engineering, some researchers suggest that bacteria can be reformed to carry more desirable gene characteristics, including the production of digestive enzymes and antimicrobial substances.
Prebiotics are aimed at supplying probi-otics with an advantageous source of nutrients, implying that their needs are different to those of the host and/or different to those of potential pathogens. Certain oligosaccharides, which resist endogenous enzyme degradation, seem to promote a more favorable microflora in the lower small intestine and also the large intestine. However, certain pathogenic bacteria, such as Clostridium perfringens are also able to ferment some of the oligosaccharides. There is some preliminary work with pigs suggesting synergism for certain combinations of prebiotics and probiotics, which is expected if both are efficacious.
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The first trimester is very important for the mother and the baby. For most women it is common to find out about their pregnancy after they have missed their menstrual cycle. Since, not all women note their menstrual cycle and dates of intercourse, it may cause slight confusion about the exact date of conception. That is why most women find out that they are pregnant only after one month of pregnancy.