Bacteria basic concepts

Bacteria Basic Concepts Bacterial Structure and Function... 

Techniques such as sterilization, pasteurization, or disinfection operate on the basis of the effects of heat, radiation, or chemical agents on viability of cells (bacteria, viruses), while filtration and membrane techniques act mainly mechanically. Even though the mechanisms of desactivation are quite different, similar basic concepts can be applied in most of these cases. 

After establishment of the basic concept of competitive exclusion, considerable research has been done to identify the mechanisms by which bacteria are competitively excluded from host sites (Nurmi et al. 1992 Zhao et al. 1995). Responsible factors include competition for receptor sites on the intestinal epithelium, production of volatile fatty acids and/or other antibacterial substances, and competition among different bacteria for limited nutrients. The use of LAB as a probiotic for live poultry and livestock has been extensively studied and has... 

In the case of rodent tests reports continue to appear that stress the effect on survival of balanced diets" and of the time of day when the animal is irradiated. Even if one allows for the obvious differences between the bacteria and mouse test systems it is unfortunate that a better correlation between the two systems does not exist, even for a single class of drugs.A modification of the basic concepts of radiation dosimetry to Include a physical quantity other than absorbed dose was recommended to permit a better correlation with biological effects. ... 

Human milk is a true prebiotic, and its neutral oligosaccharides are known as the main bifidus factor [404], which prevents digestive tract infections because it induces and improves the growth of good intestinal flora. The prebiotic concept was developed by Gibson and Roberfroid in 1995 [410]. According to their definition, a prebiotic effect is proven when bifidobacteria, lactobacilli, and other healthy bacteria are specifically stimulated and potentially harmful bacteria are depressed [411]. The concept of using prebiotics in infent formulas is related to three basic assumptions [412] ... 

Variation in Purine Synthesis. An important development in purine biochemistry came from studies on sulfonamide inhibition of bacteria. A compound was found to accumulate in cultures of E. colt incubated with sulfadiazine. This was identified as 4-aminoimidazole-5-car-boxamide. In the present concept, this compound represents a degradation product of the corresponding ribotide, but it can also be used as a purine precursor. The free imidazole reacts with ribose-l-phosphate in the presence of nucleoside phosphorylase to form a nucleoside which can be phosphorylated by a kinase. Thus, variations of the basic scheme can and do occur. 

A detailed description of the microbial populations at different sites in the mouth and on the tooth surface is beyond the scope of this book, but, reference should be made to the concept of a basic plaque community. Studies on plaques from a number of animals and reference to Table 33.2 indicate that the streptococci and Actinomyces are the best adapted of the oral bacteria and that a mixture of the two species forms the basis of a plaque composition common to all mouths. Other populations are then superimposed on this basic mixture, depending on local conditions. The relative proportions of streptococci and Actinomyces depends on the nature of the diet, a sugar-rich diet favouring the streptococci, particularly those which have the ability to produce extracellular polysaccharides from sucrose and to ferment carbohydrates to acid. 

Let us first discuss modern concepts about the genetic regulatory systems of bacteria and phage. The basic ideas were proposed by Jacob and Monod (Jacob and Monod, 1961 Jacob and Wollman, 1962 for review see Benzer, 1963 Kumar et al., 1970 Szybalski, 1972 Ratner, 1975 Flint, 1977 Smith, 1977 Nover et al., 1978). It was demonstrated that in bacteria there are blocks of contiguous structural genes which code for specific proteins and which are assembled into functional units or operons. These units participate for instance in the regulation of the synthesis of enzymes which in turn participate in lactose utilization (Fig. 94). 

Sol-gel-derived silane-based materials have been proven as a suitable matrix for entrapment of bioactive species, due to biocompatibility of silica and the mild operating conditions. We recall that the solutions used for cathodic electrochemical deposition of silane-based sol-gel films are usually mild acidic (pH 3-6), and the deposition is achieved by electrochemically driving the inter- cial pH near the cathode to mild basic, about pH 8. This environment is favorable for maintaining the activity of biological species such as proteins, enzymes, and bacteria. Many researchers have reported the fabrication of biosensing films by co-electrodeposition of silane with different bioactive substances. The essence of the concept is to entrap bioactive substances within the sol-gel matrix during... 

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