Salmonella stability

Salmonella typhimurium (stabilized TCE, preincubation assay) Gene mutation McGregor et al. 1989... 

Ashwood-Smith, M.J. (1980). Stability of frozen microsome preparations for use in the Ames Salmonella mutagenicity assay. Mutation Res. 69 199-200. 

Today, in the United States, the FDA is responsible for examining safety and efficacy data before an antibiotic or synthetic chemical may be commercialized for livestock use. This includes studies on formulations, product stability, conventional and genetic toxicity, environmental safety, metabolism, residue studies in target animals, studies on antibiotic resistance in gut microflora and on salmonella shedding in target animals. Similar requirements are part of registering these products in overseas markets. In general, after a product is discovered in the laboratory, many... 

The siderophore enterobactin (enterochelin) (64) is a cyclic lactone of three N-(2,3-dihydroxybenzoyl) L-serine moieties produced by E. coli under iron stress. Enterobactin (64) was first isolated from iron-limited cultures of Salmonella typhimur-ium [83], E. coli [84], and Aerobacter aerogenes [84]. Structural analysis has confirmed that 64 chelates iron as a hexadentate ligand via the two hydroxyl groups on each catechol moiety (see Fig. 13) [85]. Of all the siderophores characterized to date, 64 has been shown to have the highest affinity for ferric iron, with a stability constant of 1052 M 1 [86, 87], which is remarkable, considering the affinity of EDTA for iron is 27 orders of magnitude lower. In mammals, serum albumin [88] and siderocalin [89, 90] bind the hydrophobic 64 which impedes siderophore-mediated transfer of iron to bacteria. Consequently, bacteria such as E. coli and... 

Sodium lactate (3-4%) in cooked beef is effective in limiting proliferation of Salmonella typhimurium, L. monocytogenes, and E. coli 0157 H7 (Miller and Acuff, 1994). Sodium lactate (3%) added to vacuum-packaged beef top rounds is effective as an oxidant and color stabilizer for cooked beef (Maca et al., 1999 Choi and Chin, 2003). 

Fig. 5.7a. Stability study of Salmonella thyphimurium (BCR-CRM 507) at various temperatures of storage.

Great attention has been paid to HAS and their safety application in plastics and coatings. The 4-unsubstituted 2,2,6,6-tetramethylpiperidine is considered as relatively toxic, the acute oral toxicity being about 1 g/kg. The substitution in position 4 (i.e. the general mode in the synthesis of HAS for polymer purposes) dramatically improves the situation. Therefore, commercial HAS like 28 (R = H), 34,35a or 35b were approved for stabilization of packaging materials in contact with food [307]. Some data are available on properties of TEMPO (2,2,6,6-tetramethylpiperidinyl-l-oxyl) and its 4-amino or 4-hydroxy derivatives. They were found to act as weak intrinsic direct mutagens in Salmonella typhimurium. TEMPO increases intracellular hydroperoxide concentration. This may indicate its pro-oxidative effect which does not result, however, in cellular toxicity [314]. 

Stabilities of GDH s from microorganisms vary greatly. Whereas the NADP-GDH from Neurospora retains activity for several days at 50° and pH 7.2 (152), the NAD-GDH inactivates rapidly at raised temperatures and low ionic strengths, but is more stable in the presence of NAD (1 mAf) and the competitive inhibitor isophthalate (64). NAD-GDH s from lower fungi are also reported to be unstable (71), but those isolated from Clostridium SBj (35) and Peptococcus aerogenes (31) are stable at 50°, and so are the NADP-dependent enzymes of Salmonella... 

The various enzyme products are marketed on the basis of activity. Sometimes the activity is determined by a standard enzyme assay, but more frequently the activity is determined by methods based upon the industrial application of the enzyme. Large consumers with well-equipped laboratories find it expedient to purchase concentrates, but smaller plants prefer to purchase enzymes at standardized activities. Materials compatible with the intended application are added to the enzyme products by the enzyme manufacturer to adjust the activity to the required value. Stabilizers, activators and other materials to improve the response of the enzyme are also added. In the case of enzymes for food applications, the usual bacteriological tests (e.g. absence of Salmonella, gas formers, etc.) are applied to the products. 

Many authors have used the acronym ALS to refer to the enzyme that catalyzes the reaction of Fig. 2.1.1. However, since ALS refers specifically to the pathway leading to valine and leudne through the intermediate (S)-2-acetolactate, the designation AHAS better describes all products of the reaction. AHAS is present in bacteria, fungi, and plants. Many of the early kinetic, mechanistic, and structural studies were carried out with AHAS isolated and purified from enteric bacteria such as Escherichia coli and Salmonella typhimurium. Eukaryotic AHAS has proven more difficult to isolate and purify because of its reduced stability. Three AHAS isozymes have been characterized in bacteria - AHAS I, II, and III - whereas only one isozyme is known in fungi and plants. 

Genetically altered adenine phosphoribosyltransferases have been found in man 32, 33) and in Salmonella 34, 35). One type of mutation in man leads to the presence of about 20% of normal activity, while others lead to increased activity, or to variable stability to heating. Both types of mutation are inherited in an autosomal manner. 

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