摘要:

AbstractSalmonella typhimuriumperiodically confronts acid environments during its life. These situations arise in chemically compromised ponds, soil, degradative cellular organelles, host digestive systems, and may even result from byproducts of their own metabolism. The levels of acid that are encountered range from mild to extreme. As a neutralophile,S. typhimuriumprefers to grow in pH environments above pH 5.5. They can survive down to pH 4 for extended periods of time. However, the limits of endurance can be stretched if the organisms are first adapted to a moderate acid pH before exposing them to acidity below pH 4.0. This adaptation, called the acid-tolerance response (ATR), includes several log phase and stationary phase systems. Some of these systems are dependent on an alternate sigma factor for RNA polymerase called O−s, whereas other systems are O−s-independent. A key to the ATR is the synthesis of a series of acid shock inducible proteins (ASPs), 51 for log phase ATR and 15 for stationary phase ATR. Some of these ASPs require O−sfor their syndiesis; others require the participation of the ferric uptake regulator protein Fur. Effective acid tolerance involves RecA-independent DNA repair systems, iron, and facets of fatty acid metabolism. Aspects of medium composition and carbon metabolism are also known to influence the nature of acid tolerance in this organism. In addition to aiding survival in the natural non-host environment, aspects of acid tolerance are also tied to virulence, as evidenced by the involvement of the mouse virulence locusmviAand the fact that acid-sensitive strains ofS. typhimuriumexhibit reduced virulence. This review summarizes these aspects of acid adaptation and includes a discussion of acid-regulated gene expression.

ISSN:1040-841X    

DOI:10.3109/10408419509113541

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

AbstractTraditionally, microbiological testing of meat products has involved isolating microorganisms and performing specific biochemical, and in some cases serological, tests to confirm the presence or absence of suspected food-borne pathogens. Given the public attention meat products have received as sources of food-borne disease, there has been considerable interest in the application of rapid detection techniques that require hours rather than days for completion. Theoretically, rapid detection methods could reduce the time from the initial sampling to confirmation so that conclusive results would be available by the time required to process the meat product. Both direct gene probe hybridizations as well as gene amplification methods show promise as rapid detection techniques. At present, direct gene probe hybridizations are being commercially utilized to confirm the presence of a suspected pathogen. A number of gene amplification protocols for detecting food-bome bacterial pathogens have been published. However, many of these studies have utilized spiked samples rather than naturally contaminated samples and many of them have involved extended template extraction/purification methodologies. There is still only a very limited amount of information on the efficacies of the various protocols in detecting bacterial pathogens, especially toxigenicEscherichia coli, Salmonellaspp.,Campylobacterspp., andListeriaspp., in naturally contaminated food samples. In order to develop gene amplification protocols that have relevance to the meat industry, there must be a concerted effort to utilize naturally contaminated samples in the development and evaluation of protocols, as well as to initiate multilaboratory round robin evaluations of select protocols. Availability of multilaboratory tested methodologies would provide a means to design pathogen detection strategies at the quality control level rather than an end product confirmatory response to an already documented outbreak.

ISSN:1040-841X    

DOI:10.3109/10408419509113542

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

AbstractPlasmodiophorids are a monophyletic group with uncertain systematic affinities. Features of the group include cruciform nuclear division; obligate, intracellular parasitism; biflagellated, heterocont zoospores; and environmentally resistant resting spores. Economically significant members of the group includePlasmodiophora brassicae, the causative agent of clubroot of cabbage;Spongospora subterranea, the causative agent of powdery scab of potato; and two members of the genusPolymyxa, vectors for several plant pathogenic viruses.

ISSN:1040-841X    

DOI:10.3109/10408419509113543

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor