Researchers from the University of Nebraska Medical Center have teamed with the Nebraska Department of Health and Human Services and the Centers for Disease Control to determine how antibiotic-resistant bacteria develop to cause disease in humans. The investigation, which is detailed in an article in the April 27 edition of the New England Journal of Medicine, was prompted by the identification of a salmonella bacteria in a child that was more resistant than any other previously found.
Salmonella is the most common cause of foodborne-related illnesses in the United States. Outbreaks have been linked to a variety of foods, including poultry and other meats, dairy products, fresh produce and dried cereals. Salmonella typically causes short-term diarrhea in otherwise healthy individuals. Serious disease may occur in very young children, the elderly, people with impaired immune systems or people being treated with antibiotics. Salmonella also is known to cause diarrhea in animals, including cattle. The bacteria affect calves most severely.
The child who became sick lived in an area in which salmonellosis occurred in at least two cattle herds. The investigation included the evaluation of several different strains of salmonella isolated from cattle involved with the outbreak. Those strains were compared with the isolate from the boy as well as strains from the CDC and Nebraska. It is not known how the child acquired the infection.
"The feature that distinguishes this particular bacteria from others is the presence of resistance to a group of antibiotics known as cephalosporins," said Paul Fey, Ph.D., a bacteriologist at UNMC who was the principal investigator of the study. "This is particularly worrisome because there are very few other antibiotics that can be used to treat children with salmonellosis if the bacteria enters the bloodstream."
Although organisms with a similar resistance pattern have been imported into the United States on at least three previous occasions, Fred Angulo, D.V.M., of the CDC's Foodborne and Diahrreal Diseases Branch, said the child's isolate was the first example of an organism having developed this pattern of antibiotic resistance within the United States. A national surveillance program is in place to identify similar bacteria and prevent their spread.
"Keeping hot foods hot and cold foods cold, and preventing cross-contamination during food preparation can prevent the majority of foodborne diseases," said co-author Thomas Safranek, M.D., epidemiologist for the State of Nebraska. "This project demonstrates the ability of nationwide monitoring programs to detect new strains of antibiotic-resistant bacteria before they become a general threat to the public." Continued monitoring by public health officials did not find any additional cases in Nebraska.
"Recognition that this type of problem can occur on the farm and ranch is important to protect the health of farm and ranch families. I have no doubt that many people thought salmonella infection occurred only through contaminated food," said Steven Hinrichs, M.D., director of the Nebraska Public Health Laboratory at UNMC, where the tests were conducted.
The researchers found that the mechanism for antibiotic resistance was due to a bacterial virus that is capable of spreading to other bacteria. This research is important in showing how the resistance developed and in tracking further spread of the bacterial virus.
In addition to Drs. Fey and Hinrichs, other UNMC researchers involved in the study were Mark Rupp, M.D., associate professor, Department of Internal Medicine - Infectious Diseases and medical director for infection control at Nebraska Health System, and Peter Iwen, assistant professor, Department of Pathology & Microbiology.
UNMC is the only public academic health science center in the state. Through its commitment to research, education, outreach and patient care, UNMC has established itself as one of the country's leading centers for cancer research and treatment, solid organ transplantation and arthritis. During the past year, nearly $31 million in research grants and contracts were awarded to UNMC scientists, and UNMC's funding from the National Institutes of Health increased by 28 percent, going from $16.2 million to $20.7 million. UNMC's educational programs are responsible for training more health professionals practicing in Nebraska than any other institution.
NHS is the partnership of the former Clarkson Hospital, the first hospital in Nebraska, and the former University Hospital, the primary teaching facility for UNMC. The combined hospital is a 685-bed facility and serves approximately 25 percent of the Omaha-area market. NHS operates clinics and health care centers serving Omaha, Plattsmouth and Auburn in Nebraska; and Council Bluffs and Shenandoah in Iowa. In addition, NHS physicians operate more than 300 outpatient clinics in 100 communities in four states. NHS provides access to tertiary and primary care including world-class specialized treatment such as solid organ transplantation, burn care, wound care, geriatrics, bone marrow (stem cell) transplantation and other cancer treatments.