ARS | Publication request: Gastrointestinal microbial ecology and the safety of our food supply as related to Salmonella

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 1, 2007
Publication Date: November 15, 2007
Citation: Callaway, T.R., Edrington, T.S., Anderson, R.C., Byrd II, J.A., Nisbet, D.J. 2007. Gastrointestinal microbial ecology and the safety of our food supply as related to Salmonella. Journal of Animal Science. 86:163-172.

Interpretive Summary: Salmonella is a pathogen that can live within the gut of food animals without making them sick, and can be transmitted to humans through the food supply. It exists in the gut as a normal inhabitant, or as a transient visitor. Salmonella is very diverse, more than 2,500 serotypes are known to exist, and each varies in its pathogenicity to humans and the host environment that it prefers. Salmonella Enteritidis is a serotype that has spread widely through the national poultry flock in the past 50 years. One theory as to how Salmonella Enteritidis (SE) became widespread in the poultry environment is that eradication programs that eliminated Salmonella Gallinarum from commercial poultry flocks left an ecological niche that was filled by SE. We must be careful not to make a similar mistake by making changes in animal production that are not supported by science. Simply “cleaning up” the birds at laying and hatching may temporarily reduce the incidence of Salmonella, but levels will quickly rise again if no other strategies are synergistically integrated into the production scheme.

Technical Abstract: Salmonella causes an estimated 1.3 million human foodborne illnesses and more than 500 deaths each year in the U.S., representing an annual estimated cost to the economy of approximately $2.9 billion. Salmonella enterica is comprised of more than 2,500 serotypes. With this genetic and environmental diversity serotypes are adapted to live in a wide variety of hosts using non-pathogenic and pathogenic lifestyles depending on environmental conditions. Thus Salmonella presents a multi-faceted threat to food production and safety. Salmonella have been isolated from all food animals and can cause morbidity as well as mortality in swine, cattle, sheep and poultry. The link between human salmonellosis and host animals is most clear in poultry. During the early part of the 20th century a successful campaign was waged to eliminate fowl typhoid caused by Salmonella Gallinarum/Pullorum. Microbial ecology is much like macroecology; environmental niches are filled by adapted and specialized species. Elimination of S. Gallinarum cleared a niche in the on-farm and intestinal microbial ecology that was quickly exploited by Salmonella Enteriditis and other serotypes that live in other hosts, such as rodents. In the years since, human salmonellosis cases linked to poultry have increased to the point that uncooked chicken and eggs are regarded as toxic by the public. Salmonellosis caused by poultry products have increased significantly in the past 5 years, leading to an FSIS Salmonella Attack Plan that targets reducing the incidence of Salmonella in chickens below the current 19%. The prevalence of Salmonella in swine and cattle is lower, but still poses a threat to food safety and production efficiency. Thus approaches to reducing Salmonella in animals must bear in mind that the microbial ecology of the animal is a critical factor that must be accounted for when designing intervention strategies. Competitive exclusion, sodium chlorate, vaccination, bacteriophage are all strategies that can reduce Salmonella in the live animal, but it is vital to understand how they function so that we do not invoke the law of unintended consequences.