Functional screening of bacterial genome for virulence genes by transposon footprinting

Potential for development of an Escherichia coli-based biosensor for assessing bioavailable methionine: a review

Methionine is an essential amino acid for animals and is typically considered one of the first limiting amino acids in animal feed formulations. Methionine deficiency or excess in animal diets can lead to sub-optimal animal performance and increased environmental pollution, which necessitates its accurate quantification and proper dosage in animal rations. Animal bioassays are the current industry standard to quantify methionine bioavailability. However, animal-based assays are not only time consuming, but expensive and are becoming more scrutinized by governmental regulations. In addition, a variety of artifacts can hinder the variability and time efficacy of these assays. Microbiological assays, which are based on a microbial response to external supplementation of a particular nutrient such as methionine, appear to be attractive potential alternatives to the already established standards. They are rapid and inexpensive in vitro assays which are characterized with relatively accurate and consistent estimation of digestible methionine in feeds and feed ingredients. The current review discusses the potential to develop Escherichia coli-based microbial biosensors for methionine bioavailability quantification. Methionine biosynthesis and regulation pathways are overviewed in relation to genetic manipulation required for the generation of a respective methionine auxotroph that could be practical for a routine bioassay. A prospective utilization of Escherichia coli methionine biosensor would allow for inexpensive and rapid methionine quantification and ultimately enable timely assessment of nutritional profiles of feedstuffs.

Development of Salmonella strains as cancer therapy agents and testing in tumor cell lines

Despite significant progress in the development of new drugs and radiation, deaths due to cancer remain high. Many novel therapies are in clinical trials and offer better solutions, but more innovative approaches are needed to eradicate the various subpopulations that exist in solid tumors. Since 1997, the use of bacteria for cancer therapy has gained increased attention. Salmonella Typhimurium strains have been shown to have a remarkably high affinity for tumor cells. The use of bacterial strains to target tumors is a relatively new research method that has not yet reached the point of clinical success. The first step in assessing the effectiveness of bacterial tumor therapy will require strain development and preclinical comparisons of candidate strains, which is the focus of this chapter. Several investigators have developed strains of Salmonella with reduced toxicity and capacity to deliver anti-tumor agents. Although methods for obtaining safe therapeutic strains have been relatively successful, there is still need for further genetic engineering before successful clinical use in human patients. As described by Forbes et al. in 2003, the main stumbling block is that, while bacteria preferentially embed within tumor cells, they fail to spread within the tumor and finish the eradication process. Further engineering might focus on creating Salmonella that remove motility limitations, including increased affinity toward tumor-generated chemotactic attractants and induction of matrix-degrading enzymes.

Perspectives on the use of organic acids and short chain fatty acids as antimicrobials

Organic acids have a long history of being utilized as food additives and preservatives for preventing food deterioration and extending the shelf life of perishable food ingredients. Specific organic acids have also been used to control microbial contamination and dissemination of foodborne pathogens in preharvest and postharvest food production and processing. The antibacterial mechanism(s) for organic acids are not fully understood, and activity may vary depending on physiological status of the organism and the physicochemical characteristics of the external environment. An emerging potential problem is that organic acids have been observed to enhance survivability of acid sensitive pathogens exposed to low pH by induction of an acid tolerance response and that acid tolerance may be linked to increased virulence. Although this situation has implications regarding the use of organic acids, it may only apply to circumstances in which reduced acid levels have induced resistance and virulence mechanisms in exposed organisms. Evaluating effectiveness of organic acids for specific applications requires more understanding general and specific stress response capabilities of foodborne pathogens. Development and application of molecular tools to study pathogen behavior in preharvest and postharvest food production environments will enable dissection of specific bacterial genetic regulation involved in response to organic acids. This could lead to the development of more targeted strategies to control foodborne pathogens with organic acids.