NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665

February 18, 1999

Antibiotic-Resistant Salmonella an Emerging Threat in North Dakota

A form of salmonella that is resistant to most antibiotics and that is sweeping across Europe is turning up in North Dakota, scientists at North Dakota State University say.

Salmonella typhimurium DT104 is usually resistant to at least five different antibiotics and is more resistant to disinfectants and environmental conditions such as heat that normally can kill. DT104 may also be more virulent than the usual strains.

"In other words, this bacterium is better able to cause disease which is harder to treat than the usual salmonella," says NDSU microbiologist Lisa Nolan .

DT104 was first detected in North Dakota by Nolan and other NDSU scientists who were studying how salmonella survives in healthy pigs. That was in 1995. The first outbreak of DT104 in humans in the United States was in Nebraska in 1996. Since then, DT104 has been detected across the country. The Centers for Disease Control and Prevention in Atlanta says it is responsible for thousands of human illnesses in the United States each year.

In North Dakota, there have been at least six livestock outbreaks of DT104-caused disease this year, according to Neil Dyer, a pathologist with the NDSU Livestock Diagnostic Laboratory.

"It's likely there were more cases than that, but unless we see something unusual in terms of antibiotic resistance, we don't test for DT104," Dyer says.

In Europe, DT104 has been a threat for more than a decade, says Nolan. First detected in Europe in the early 1980s, "DT104 really took over the salmonella business," Nolan says. By 1993, DT104 accounted for more than 80 percent of all salmonella cases diagnosed in humans in the United Kingdom.

"This form of Salmonella is doubly frightening," Nolan says. "First, it's resistant to many common antibiotics and it seems to have a propensity for picking up resistance for other antibiotics and treatments. Second, there's some indication that it's more virulent that our standard forms of salmonella." Currently there are only two forms of antibiotics commonly used against salmonella that DT104 is sensitive to, but there are indications that the organism may be building resistance to those as well.

Some researchers speculate that excessive use of antibiotics in humans and animals may speed the emergence of resistant forms of pathogens like DT104 by killing off competing organisms and selecting for the resistant bacteria. In an environment free from that competition, antibiotic-resistant pathogens thrivereproducing and spreading rapidly.

That scenario has prompted calls for an end to the use of antibiotics as growth promotants in livestock production and stricter controls on antibiotic use in both humans and animals.

Nolan's research team is working with Dave White of the U.S. Food and Drug Administration on research funded by the National Pork Producers' Council. They are studying the basic biological mechanisms that DT104 uses to protect itself from antibiotics. "That research is just getting underway, but if we can understand how resistance works we might be able to interrupt it or find some way around it," Nolan says. Although the research focuses on pigs, salmonella is common to all livestock and humans. "Advances in one species will have implications across the board," she says.

DT104 affects humans like other forms of Salmonella, causing flu-like symptoms which pass in a few days. In the elderly, young and those with suppressed immune systems, salmonella can be devastating, causing diarrhea, fever and dehydration and may result in hospitalization. Salmonella is sometimes found in eggs, raw and undercooked poultry and meat. Protect yourself by cooking chicken and eggs thoroughly, cleaning cutting boards, counter tops, plates and utensils and by cooling leftover food promptly.

###

Sources: Lisa Nolan (701) 231-8530 and Neil Dyer (701) 231-7521

Editor: Tom Jirik (701) 231-9629