Gastrointestinal microbial ecology and the safety of our food supply as related to Salmonella

¹ Agricultural Research Service, Food and Feed Safety Research Unit, College Station, TX, 77845

^* To whom correspondence should be addressed. E-mail: callaway{at}ffsru.tamu.edu.

	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 $2.4 billion. Salmonella enterica is comprised of more than 2,500 serotypes. With this genetic and environmental diversity, serotypes adapted to live in a wide variety of hosts which may or may not manifest themselves with clinical illness. 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 Enteritidis 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 in the zeitgeist. Salmonellosis caused by poultry products have increased significantly in the past 5 yr, leading to a USDA Food Safety and Inspection Service "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. Use of competitive exclusion, sodium chlorate, vaccination, and 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.

Key Words: ecology, intestinal, reduction, Salmonella