Salmonella definition

In most instances the test system will be self-evident (e.g., the animal to which the test article is administered or applied). Studies with micro-organisms, however, sometimes present difficulty in defining the test system. In the case of the Ames test, for example, the test system is not merely the colonies of salmonella or yeast, but includes in addition the culture medium, metabolic activation agent (if any), biotin, histidine, and buffer (if any). The last sentence of the definition makes it clear that untreated control groups also meet the definition of test system even though a test or control article is not administered or applied to such groups. 

A number of issues were addressed in the general sessions that were common to all six of the proposed protocols. These included definitions of each of the sample media, limitations of the protocols, guidelines for the fractionation of samples found to be toxic in the Salmonella assay, and analytical quality control considerations. 

The untreated SRC-II was tested at five concentrations with Salmonella strains TA 98 and TA 100, generally considered the most sensitive strains. In the results indicated in Table III, an increase in the number of revertants greater than two times the background (no SRC-II feed or product) is sometimes considered to indicate a definite positive (mutagenic) response. The plates which showed a positive response by this criteria are underlined. 

Indeed, symptoms of pathogen-specific enteritis are not sufficiently unusual to distinguish a disorder form those due to Salmonella, Shigella, Campylobacter or Yersinia or other pathogens. The combination of fever and faecal leukocytes or erythrocytes is indicative of inflammatory diarrhoea,but the definite diagnosis is based on culture or demonstration of specific organisms on stained faecal smears. 

In summary, the levels of NAD in Salmonella typhimurium appear to be regulated boA by feedback inhibition as well as by repression. The structural genes for the proteins that are involved in these regulatory mechanisms have been identified, although a detailed biochemical characterization of the nadl repressor protein and a definition of the regulatory site on the nadB enzyme remain to be carried out. 

The limits of the sensitivity of the standard pol A procedure (lowest effective dose) for a number of chemicals have been compared to the dose required to give a positive test in the Salmonella mutagenicity assay (Table 5). For the chemicals selected that are active in both systems, it was found that there was no definite trend. The Salmonella assay was exquisitely sensitive to some chemicals (e.g., aflatoxin Bi), while the pol A system responded to low levels of others (e.g., mitomycin C). 

The mechanism for the polymerization of the teichoic acids has not been definitively established, but it is most probably very similar to the biosyntheses of the other lipid-coenzyme-dependent polysaccharides, the peptidomurein and Salmonella 0-antigen polysaccharide, in which the monomer unit or repeating unit attached to the lipid polyprenol pyrophosphate carrier is inserted between the growing chain and the lipid coenzyme carrier. See Fig. 10.12B for the proposed mechanism for teichoic acid biosynthesis. 

The above ranges assume that other growth factors are optimal but clearly they will narrow as combinations of stresses are introduced. However, there is a lack of information about such interactions between the various environmental factors and their effects on the growth limits of salmonellae, and this is a research area which merits further quantitative definition. It should then be feasible to design and formulate new food products, within organoleptic constraints, which would not intrinsically support the multiplication of salmonellae . Many conventional foods and raw materials, however, provide ideal substrate conditions for growth of salmonellae and it is not practical or economic to alter their composition without loss of marketable character. In such cases, control can best be achieved by manipulation of extrinsic environmental factors (with emphasis on... 

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