New Technologies Question the Equality of Pathogens

In late 2001, A United States appeals court ruled that the U.S. Dept. of Agriculture's Food Safety and Inspection Service could not shut down plants under its jurisdiction for failing to meet the "Salmonella performance standard."FSIS has indicated that it won't pursue further legal action, but will now consider unsatisfactory Salmonella results a red flag of sorts and will place an offending plant under increased regulatory scrutiny.

Consumer groups were outraged by the court ruling, as it was read by some as caveat emptor, let the consumer beware. But which, in light of current science, is reasonable the court ruling or FSIS's proposed regulatory action? Is the mere presence of Salmonella in any product sufficient grounds for regulatory action? And what of other USDA and Food and Drug Administration policies regarding presence/absence regulation for microorganisms?

Current science, including the application of genetic technologies, coupled with greater data-gathering and surveillance capability, as well as enhanced access to human, animal, plant, and environmental bacterial isolates, may be suggesting that future regulation of food for certain pathogens on a presence/absence basis may not be appropriate. These scientific developments are having and will have tremendous regulatory impact in the coming decade.

In late 2001, A.R. Sawari and coauthors, writing in the Journal of Infectious Diseases (Vol. 183, pp. 2195-2199), noted that the serotype distribution of Salmonella isolates from slaughtered food animals differs significantly from that from humans. Therefore, questions are raised as to whether (1) raw animal products are the primary source of human salmonellosis, (2) the risk of transmission to humans is equal for all food categories, and (3) all Salmonella serotypes have an equal ability to cause human illness. While these questions persist, it would appear that several regulatory policies assume that they are fact.

IFT's recently published Expert Report, "Emerging Microbiological Food Safety Issues: Implications for Control in the 21st Century"(www.ift.org/govtrelations/microfs/) addresses the advances in surveillance and applied genetic technologies and how they may impact regulatory thinking. Our understanding of Salmonella virulence is complicated by the fact that Salmonella contain more than 200 virulence factors. Further, not all Salmonella may contain all possible virulence factors, and Salmonella may therefore be virulent, relatively avirulent, or aviru-lent for humans, depending on which virulence genes they possess and express. Only time and the application of knowledge gained from genomic studies will help us better understand Salmonella virulence.

A situation somewhat parallel to that for Salmonella would appear to be present for Listeria monocytogenes as well. The bacterium is not tolerated in ready-to-eat foods within the limits of the test and sample size. There is the apparent belief that all L. monocytogenes serotypes are equally virulent for humans. Its near ubiquity in the environment assures that it will be present in raw foods, and even in cooked, ready-to-eat foods, at some level and frequency. Its widespread occurrence in the food supply also suggests that most humans are regularly exposed to some level of the bacterium through the food they eat, yet do not become ill. Predisposing factors in some subpopulations may render those individuals more susceptible to infection by L. monocytogenes, or perhaps, as has been suggested for Salmonella, not all L. monocytogenes are equally virulent.

Recent studies using new genetic technologies suggest that perhaps all L. monocytogenes are not of equal virulence, and moreover, that many food isolates are of a genetic type that suggests that they are not virulent for humans. Numerous regulatory actions have been taken against smoked fish producers when L. monocytogenes has been isolated from finished product. Yet a 2001 report by D.M. Norton and coworkers in Applied Environmental Microbiology (Vol. 67, pp. 646-653) suggests that the majority of isolates from the smoked fish industry do not genetically cluster with L. monocytogenes strains that have caused epidemic-scale outbreaks, and further, that they have a reduced or absent ability to form plaques in an in-vitro virulence assessment assay.

The regulatory impact of the science described above and the policy questions that science raises assure lively debates in the future and also point to other promising avenues of research using the new tools that are revolutionizing our thinking about pathogens. We should be grateful that the science is advancing our knowledge, and see where the advances in science lead us. As with most things in science, before a definitive answer is reached (if indeed it can be), more research will be driven by the many questions that will be raised.

by DOUGLAS L. ARCHER
Contributing Editor
Professor, Food Science and Human Nutrition Dept.
University of Florida