摘要:

AbstractImprovement of the antibiotic yield of industrial strains is invariably the main target of industry-oriented research. The approaches used in the past were rational selection, extensive mutagenesis, and biochemical screening. These approaches have their limitations, which are likely to be overcome by the judicious application of recombinant DNA techniques. Efficient cloning vectors and transformation systems have now become available even for antibiotic producers that were previously difficult to manipulate genetically. The genes responsible for antibiotic biosynthesis can now be easily isolated and manipulated. In the first half of this review article, the limitations of classical strain improvement programs and the development of recombinant DNA techniques for cloning and analyzing genes responsible for antibiotic biosynthesis are discussed. The second half of this article addresses some of the major achievements, including the development of genetically engineered microbes, especially with reference toβ-lactams, anthracyclines, and rifamycins.

ISSN:1040-841X    

DOI:10.3109/10408419609105481

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe bacterial pathogenClostridium perfringensis the most prolific toxin-producing species within the clostridial group. The toxins are responsible for a wide variety of human and veterinary diseases, many of which are lethal.C. perfringenstype A strains are also associated with one of the most common forms of food-borne illness (FBI). The toxicosis results from the production and gastrointestinal absorption of a protein-enterotoxin known as CPE. The regulation, expression, and mechanism of action of CPE has been of considerable interest as the protein is unique. CPE expression is sporulation associated, although the mechanism ofcpe-gsne regulation is not fully elucidated. Cloning studies suggest the involvement of global regulators, but these have not been identified. Although very few type A strains are naturally enterotoxigenic, thecpegene appears highly conserved. In FBI strains,cpeis chromosomally encoded; whereas in veterinary strains,cpemay be plasmid-encoded. Variation incpelocation suggests the involvement of transposable genetic element(s). CPE-like proteins are produced by some C.perfringenstypes C and D; and silent remnants of thecpegene can be found in C.perfringenstype E strains associated with the iota toxin gene. CPE has received attention for its biomedical importance. The toxin has been implicated in sudden infant death syndrome (SIDS) because of its superantigenic nature. CPE can destroy a wide variety of cell types bothin vitroandin vivo, suggesting that it could have potential in the construction of immunotoxins to neoplastic cells. It is obvious that CPE is an interesting protein that deserves continued attention.

ISSN:1040-841X    

DOI:10.3109/10408419609105482

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractRegulatory programs and guidelines for the control of foodborne microbial agents have existed in the U.S. for nearly 100 years. However, increased awareness of the scope and magnitude of foodborne disease, as well as the emergence of previously unrecognized human pathogens transmitted via the foodborne route, have prompted regulatory officials to consider new and improved strategies to reduce the health risks associated with pathogenic microorganisms in foods. Implementation of these proposed strategies will involve definitive costs for a finite level of risk reduction. While regulatory decisions regarding the management of foodborne disease risk have traditionally been done with the aid of the scientific community, a formal conceptual framework for the evaluation of health risks from pathogenic microorganisms in foods is warranted. Quantitative risk assessment (QRA), which is formally defined as the technical assessment of the nature and magnitude of a risk caused by a hazard, provides such a framework. Reproducing microorganisms in foods present a particular challenge to QRA because both their introduction and numbers may be affected by numerous factors within the food chain, with all of these factors representing significant stages in food production, handling, and consumption, in a farm-to-table type of approach. The process of QRA entails four designated phases: (1) hazard identification, (2) exposure assessment, (3) dose-response assessment, and (4) risk characterization. Specific analytical tools are available to accomplish the analyses required for each phase of the QRA. The purpose of this paper is to provide a description of the conceptual framework for quantitative microbial risk assessment within the standard description provided by the National Academy of Sciences (NAS) paradigm. Each of the sequential steps in QRA are discussed in detail, providing information on current applications, tools for conducting the analyses, and methodological and/or data limitations to date. Conclusions include a brief discussion of subsequent uncertainty and risk analysis methodologies, and a commentary on present and future applications of QRA in the management of the public health risks associated with the presence of pathogenic microorganisms in the food supply.

ISSN:1040-841X    

DOI:10.3109/10408419609105483

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractMany of the parasitic protozoa, such asEntamoeba histolytica, Giardia, Trypanosoma, Leishmania, andPlasmodium, are considered to be anaerobes because they can be grownin vitroonly under conditions of reduced oxygen tension. However, these parasitic protozoa have been found to be aerotolerant or microaerophilic, and also to consume oxygen to a certain extent. Furthermore, these organisms are highly susceptible to exogenous reactive oxygen species, such as hydrogen peroxide. They must, therefore, detoxify both oxygen and free radical products of enzymatic reactions. However, they lack some or all of the usual antioxidant defense mechanisms present in aerobic or other aerotolerant cells, such as catalase, superoxide dismutase, reduced glutathione, and the glutadiione-recycling enzymes glutathione peroxidase and glutathione reductase. Instead, they possess alternative mechanisms for detoxification similar to those known to exist in certain prokaryotes. Although the functional aspects of these alternative mechanisms are yet to be understood completely, tiiey could provide new insights into the biochemical peculiarities of these enigmatic pathogens.

ISSN:1040-841X    

DOI:10.3109/10408419609105484

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor