Salmonella discussion

Each year in the United States, approximately 76 million food-borne illnesses occur, leading to 325,000 hospitalizations and over 5000 deaths.40 A number of bacterial and viral pathogens that have been discussed previously in this chapter (e.g., Salmonella, Shigella, Campylobacter, E. coli, and noroviruses) can cause food poisoning. Other bacteria that can cause foodborne illness include Staphylococcus aureus, C. perfringens, C. botu-linum, and Bacillus cereus (Table 73-5). Food poisoning should be suspected if at least two individuals present with similar symptoms after the ingestion of a common food in the prior 72 hours. 

These examples illustrate the power of proper ANN feature space optimization. In all the examples discussed, the limits of the type of information that could be gleaned from the Salmonella PyMAB spectra were probed. The PD-ANN s automated optimization removed the issue of methodological uncertainty and enabled a focus on questions of Py-MAB-MS spectral information content and its potential use for rapid strain ID. Question Does Py-MAB-MS data support Serovar classification Answer Yes. How about PFGE classification Yes. How about antibiotic resistance profile Answer Perhaps, if one first eliminates stronger contributions to spectral variation and then, by design and grouping, limits the possibilities to only a few classes. 

McCann, J. and Ames, B.N., Detection of carcinogens as mutagens in the Salmonella/micro-some test assay of 300 chemicals discussion, Proc. Natl. Acad. Sci. USA, 73, 950, 1976. 

Examples of killed or inactivated vaccines are cholera vaccine containing dead strains of Vibrio cholerae, hepatitis A vaccine with inactivated hepatitis A virus, pertussis vaccine with killed strains of Bordetella pertussis, typhoid vaccine with killed Salmonella typhi, and influenza vaccine with various strains of inactivated influenza viruses (see Exhibit 4.2 for a discussion of influenza viruses and vaccines and Exhibit 4.3 on avian influenza H5N1). 

McCann, ). and Ames, B. N., Discussion Paper The Detection of Mutagenic Metabolites of Carcinogens in Urine with the Salmonella/Microsome Test, Ann. N.Y. Acad. Sci. (1975) 269, 21. 

Protocols for preparing six environmental sample types prior to the Ames Salmonella assay were proposed at a recent panel discussion sponsored by the U.S. Environmental Protection Agency (USEPA) and the U.S. Army. Air particles, soil-sediment, and solid waste are extracted with dichloromethane, concentrated, and solvent exchanged into dimethyl sulfoxide (DMSO). Organics in water and waste water are absorbed onto XAD columns, then eluted with hexane-acetone, solvent reduced, and exchanged into DM SO. Nonaqueous liquids are assayed directly and as concentrates before they are solvent exchanged to DMSO. If bacterial toxicity or lack of dose response is observed in the Ames assay of extracts, the extracts are fractionated prior to solvent exchange. These are interim methods and have not been subjected to policy review of the USEPA or the U.S. Army. 

Characterization of Organic Mutagens. The chemical analyses (GC-MS) still leave the identity of the mutagens just discussed untouched. Therefore, further characterization was attempted by using specific enzyme-deficient strains of Salmonella. A first indication of the nature of some of these compounds was recently obtained by testing organic drinking water concentrates with the nitroreductase-deficient (NR-) strains of Salmonella that were isolated by Rozenkranz et al. (16). 

The need for shortening the time and increasing the sensitivity for detection of antigens has lead to development of different amplification systems. Some of the initial efforts focused on use of more pure antibodies (59, 60), more specific monoclonal over less specific polyclonal antibodies (61) and use of a combination of monoclonal antibodies (62). The next phase saw the incorporation of labels as discussed in the previous section. The use of labels does increase the sensitivity however, there is a need to go down in detection levels to enable faster turnaround time for immunoassays. This can mean significant savings in the food industry. In the case of Salmonella, the assay time is being reduced from several days to less than a day (63, 64). 

Of the lipid portions of bacterial macromolecular amphiphi-les, that of lipopolysaccharides is the structurally most complex. For its designation the term lipid A has been coined. More specifically, it was suggested that the lipid, as it is present in intact lipopolysaccharide, should be called lipid A, while the lipid in a separated form should be termed free lipid A (10,11). This nomenclature will be used throughout this paper. In the following, ways and methods will be described which have been used to elucidate the chemical structure of lipid A. The present discussion will deal in more detail with the elucidation of the structure of Salmonella lipid A. Relative to this structure, chemical features of other lipid A s will then be discussed. 

In light of this new evidence the Salmonella lipid A structure (Fig. 6) requires certain modifications. A proposal for the chemical structure of Salmonella lipid A which takes in account the above discussed new findings and which is in accord with the present knowledge is presented in Fig. 8. 

In some cases, chemicals are known to be carcinogens from epidemiological studies of exposed humans. Animals are used to test for carcinogenicity, and the results can be extrapolated with some uncertainty to humans. The most broadly applicable test for potential carcinogens is the Bruce Ames procedure, which actually reveals mutagenicity. The principle of this method is the reversion of mutant histidine-requiring Salmonella bacteria back to a form that can synthesize their own histidine.12 The test is discussed in more detail in Section 8.4. 

In 1967, two possible general mechanisms for the biosynthesis of linear polysaccharides were proposed.86 The first was the primer mechanism already discussed, and the second was the sequential addition of monomer units to the reducing end by the insertion between a carrier and the growing polysaccharide chain. This latter mechanism had been shown for Salmonella sp. O-antigenic polysaccharide87 then in 1973, it was shown for the bacterial cell-wall polysaccharide murein88 in which the carrier was a polyisoprenoid pyrophosphate. 

The purpose of this chapter is to describe the competition for iron between iron-binding proteins of the animal and the siderophores of bacterial parasites. This discussion will be limited to two bacterial species—a slow-growing organism Mycobacterium tuberculosis and a fast-growing organism Escherichia coli. Both organisms produce specific siderophores which have been defined chemically and physically. Myco-bactin, the siderophore of M. tuberculosis, because of its hydrophobic nature, is associated mostly with the lipoidal cell wall of the tubercle bacillus (11) whereas enterochelin (enterobactin), the siderophore of E. coli and Salmonella typhimurium, is soluble in water and is rapidly lost by the bacterial cell into the surrounding medium (12, 13). 

Figure 10 A schematic drawing of the cell envelope of E. coli consisting of the cytoplasmic membrane, the periplasm, and the outer membrane. Various proteins are shown, sets of which represent specific siderophore-transport systems. Outer-membrane receptors (OMR) shown here are FepA (enterobactin), lutA (aerobactin), Fee A (Fe dicitrate), FhuA (ferrichrome), and FhuE (coprogen, Fe rhodotorulate, and ferrioxamine B). FoxA (ferrioxamine B), is not a receptor of E.coli, but of the closely related Salmonella. Not shown here are the receptors Fiu and Cir (Fe (DHBS) n indicates 3 possible linear degradation products of enterobactin) and FeO, a transport system for Fe . Details are discussed in Section 5.1...

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