Germ Warfare: Penn Researchers Collaborate on Nationwide Salmonella Study
By Alan Atchison
The Centers for Disease Control and Prevention (CDC) estimates that food poisoning causes 76 million illnesses, 325,000 hospitalizations and as many as 5,000 deaths in the United States each year. Some of the most common bacterial forms of infection, the salmonellae organisms, account for $1 billion in medical costs and lost work time.
In what originated as a grant proposal funded by the Commonwealth of Pennsylvania Bureau of Animal Health in 2002, scientists at Penn Vet's New Bolton Center began work on a Salmonella typing system, work that is growing into a major collaborative effort.
Penn Vet is using the standardized protocols of a national molecular subtyping network for food-borne bacterial disease surveillance called PulseNet. Developed in 1995 by the CDC and the Association of Public Health Laboratories, PulseNet was designed to track various food-borne, disease-causing bacteria. By the start of 2004, PulseNet was being used in laboratories throughout the country and now also operates internationally.
Dr. Charles Benson, professor of microbiology, and Mr. Donald Munro, retired from the Scottish Salmonella Reference Laboratory in Glasgow, head the Salmonella Reference Center at New Bolton Center in Kennett Square, Pa. Dr. Benson and Mr. Munro have amassed a Salmonella culture collection of more than 25,000 isolates. In 2002 Dr. Shelley Rankin, assistant professor/clinician educator of microbiology, along with Dr. Benson and Mr. Munro, developed a database for Salmonella pulse-field gel electrophoresis (also referred to as "DNA fingerprinting") in accordance with the CDC PulseNet model. Currently, DNA fingerprints have been created and stored on nearly 2,000 Salmonella isolates. This database has been used to characterize Salmonella outbreaks on Pennsylvania farms. One particular study even led to collaboration with the CDC to investigate a milk-borne outbreak of Salmonella typhimurium. It has also been found that multiple strains of Salmonella newport can be identified in animals in Pennsylvania. Due to the high prevalence of Salmonella newport, the timely recognition of these strains offers a huge advantage to the agricultural community, as appropriate treatment for afflicted animals drastically lessens the possibility of economic loss and widespread disease.
Dr. Rankin, who refers to herself as the "keeper of the database," was an invited speaker at the Seventh Annual PulseNet Update Meeting in 2003 and also presented data on Salmonella newport to the Massachusetts State Department of Public Health at its request. This past May, the Salmonella Reference Center at New Bolton Center was asked to be the first laboratory in the USDA–VetNet program. USDA-VetNet, headed by microbiologist Dr. Paula Fedorka-Cray in Georgia, is working to identify Salmonella strains in slaughter/processing plants that potentially could cause illness in humans.
Dr. Rankin also is part of the Pennsylvania Antimicrobial Resistance Study Group, formed by Dr. Nkuchia M'ikanatha, an epidemiologist at the Pennsylvania Department of Health. This study group is represented by the University of Pennsylvania Schools of Veterinary Medicine and Medicine, the university's Center for Clinical Epidemiology and Biostatistics, the Pennsylvania Department of Agriculture, the Pennsylvania Department of Health, the CDC and the Food and Drug Administration Center for Veterinary Medicine. The group is studying the presence and spread of antibiotic-resistant Salmonella in chicken in comparison with antibiotic-resistant salmonellosis in humans.