Nontyphoidal Salmonellae are responsible for an estimated 1.4 million cases of gastrointestinal disease with 500 associated deaths in the United States, at a cost of $2 billion. The number of cases worldwide probably exceeds 100 million each year. Infection generally occurs after the ingestion of contaminated food or water, and usually leads to a self-limiting enterocolitis. The disease is characterized by diarrhea, abdominal cramps, nausea, fever, vomiting, and headache lasting 7–10 days, followed by a longer period of subclinical fecal shedding. Infants, the elderly, and immunocompromised individuals are at risk for serious systemic complications and death as a result of infection.
Contaminated foods, including beef, pork, poultry, and egg products are frequent vectors responsible for the transmission of these organisms to humans. Livestock can harbor Salmonellae subclinically resulting in carcass contamination at slaughter and in the laying of contaminated eggs. In recent years, as the traditional routes of infection are better controlled, large outbreaks of nontyphoidal Salmonella infection in the United States have been attributed to fruits, vegetables, and processed foods including jalapeño peppers, cantaloupe, cereal, and peanut butter (CDC).
Serology based on surface antigens is the standard method of classification of Salmonella. The host-range and disease can differ considerably between serovars, making such classification important. Throughout the world, the most prevalent nontyphoidal serovars isolated from human sources are serovars Typhimurium and Enteritidis and these two serovars comprise nearly 40% of isolations from human sources in the United States. These serovars can be harbored subclinically in livestock for prolonged periods of time and are thus very difficult to eradicate in the absence of a detailed knowledge of the biology of the organism in this niche.
The bacterial factors necessary for Salmonellae to persist subclinically in the gastrointestinal tract of livestock and to survive and grow in other reservoirs such as crops and processed foods are only beginning to be elucidated. This knowledge will allow the development of new strategies and the identification of points in the production chain where producers can intervene to improve the safety of foods. We review the current status as well as the uses of complete genome sequence information for Salmonellae, and enhancements of genetic techniques that may rapidly increase our knowledge of the biology of this organism in these important food safety niches.
Complete genome sequencing of Salmonellae is allowing us to better understand their genetic diversity, to develop novel tools, and to improve existing genetic techniques to understand the complex biology of these important food-borne pathogens. Approximately half of the genes in Salmonella still have no known phenotype in the environment. Frontiers for further study of Salmonella for improved food safety using modern genetic tools are likely to include determination of the genes necessary for environments where Salmonella must survive outside the host, such as in feces, soil, water, and plants. Understanding how Salmonella completes its entire host-to-host life cycle in agriculture may reveal previously unknown vulnerabilities that will be susceptible to novel intervention and allow us to break the chain of transmission.
Novel genetic tools for studying food-borne Salmonella. Curr Opin Biotechnol. 2009 Apr;20(2):149-57.
Nontyphoidal Salmonellae are highly prevalent food-borne pathogens. High-throughput sequencing of Salmonella genomes is expanding our knowledge of the evolution of serovars and epidemic isolates. Genome sequences have also allowed the creation of complete microarrays. Microarrays have improved the throughput of in vivo expression technology (IVET) used to uncover promoters active during infection. In another method, signature tagged mutagenesis (STM), pools of mutants are subjected to selection. Changes in the population are monitored on a microarray, revealing genes under selection. Complete genome sequences permit the construction of pools of targeted in-frame deletions that have improved STM by minimizing the number of clones and the polarity of each mutant. Together, genome sequences and the continuing development of new tools for functional genomics will drive a revolution in the understanding of Salmonellae in many different niches that are critical for food safety.
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Malaria and alcohol consumption both represent major public health problems. Alcohol consumption is rising in developing countries and, as efforts to manage malaria are expanded, understanding the links between malaria and alcohol consumption becomes crucial. Our aim was to ascertain the effect of beer consumption on human attractiveness to malaria mosquitoes in semi field conditions in Burkina Faso. We used a Y tube-olfactometer designed to take advantage of the whole body odour (breath and skin emanations) as a stimulus to gauge human attractiveness to Anopheles gambiae (the primary African malaria vector) before and after volunteers consumed either beer (n = 25 volunteers and a total of 2500 mosquitoes tested) or water (n = 18 volunteers and a total of 1800 mosquitoes). Water consumption had no effect on human attractiveness to An. gambiae mosquitoes, but beer consumption increased volunteer attractiveness. Body odours of volunteers who consumed beer increased mosquito activation (proportion of mosquitoes engaging in take-off and up-wind flight) and orientation (proportion of mosquitoes flying towards volunteers’ odours). The level of exhaled carbon dioxide and body temperature had no effect on human attractiveness to mosquitoes. Despite individual volunteer variation, beer consumption consistently increased attractiveness to mosquitoes. These results suggest that beer consumption is a risk factor for malaria and needs to be integrated into public health policies for the design of control measures.
