Northwestern Researchers Develop Rapid Diagnostic Test To Detect Antibiotic-Resistant Bacteria

May 18, 1998

CHICAGO --- Researchers at Northwestern University Medical School have greatly improved upon a method used to diagnose an antibiotic-resistant bacteria seen in hospitalized patients. They have reduced from 48 to 8 hours the time needed to identify the potentially lethal bacteria, known as vancomycin-resistant enterococci, or VRE.

A report on the technique, which detects and amplifies even very minute quantities of the genes for two types of this bacteria, vanA and vanB, will be presented at the American Society for Microbiology's annual meeting in Atlanta on May 17-21. Valentina Stosor, M.D., an instructor in the department of medicine at the Medical School, was lead investigator on the Northwestern study and will present the report.

The researchers also showed that the new method, called hot-start polymerase chain reaction (PCR), detected vanA and vanB in 13 of 15 specimens versus 12 of 15 specimens detected using the standard culture method. Combining the methods resulted in detection in 14 of 15 cases.

The prevalence of antibiotic-resistant bacteria poses a growing threat to hospital patients. Because VRE are immune to all currently available antibiotics, it is vitally important to isolate patients with VRE as quickly as possible, according to the Centers for Disease Control and Prevention (CDC).

Like standard PCR, the hot-start method is used to amplify, or produce numerous copies of, a specific segment of DNA. However, a drawback to the older PCR method is that it often replicates other nonspecific strands of DNA. The newer hot-start method not only cut down on nonspecific binding, but also increased the yield of the PCR, Stosor reported.

The standard method of identifying bacteria requires patient samples to be grown in culture. In addition to the lengthy period needed to grow the bacteria, small sample size, low organism density and overgrowth by other contaminants make reading the culture difficult.

"Detection of the infection nearly two days earlier allows isolation and treatment to begin immediately. In addition, early isolation prevents the VRE from exchanging their resistance with other bacteria," Stosor said.

Gary A. Noskin, M.D., associate professor of medicine, Lance R. Peterson, M.D., professor of pathology, and Michelle A. Tornatore, research technologist, of Northwestern University Medical School, and F.C. Tenover, chief of the Nosocomial Pathogens Laboratory Branch at the CDC, were co-investigators on this project.


(Editor's note: Dr. Stosor can be reached during the American Society for Microbiology meeting in Atlanta at the Westin Peachtree Plaza, 404-659-1400. Dr. Peterson can be reached at the Omni Hotel at CNN Center, 404-659-0000. Dr. Noskin can be reached at Northwestern University Medical School at 312-908-2729 or e-mail at

Northwestern News on the World Wide Web:
CONTACT: Elizabeth Crown at (312) 503-8928 or e-mail at

Northwestern University

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