In a development unusual in an era when most disease-causing agents have already been found, government researchers have identified a new bacterium that causes a serious lymph node infection in some patients with suppressed immune systems.
"The discovery of new bacteria is not uncommon, but discovering an organism that causes human illness is certainly unique," said Dr. Elias A. Zerhouni, director of the National Institutes of Health.
The bacterium has been found in three patients with chronic granulomatous disease, which affects an estimated one person in 250,000. But researchers said the source of at least half of all infections in such patients could not be identified in the past, suggesting that the bacterium could be common in this population.
The immunodeficiency disease is caused by a genetic defect in an enzyme called phagocyte NADPH oxidase, which is used in immune cells to generate hydrogen peroxide that kills bacteria and fungi.
In July 2003, a 39-year-old man with chronic granulomatous disease was referred to the NIH after three months of unexplainable fever, chills, fatigue and night sweats, in addition to a 10-pound weight loss. Antibiotics did no good. Two months later, he experienced painful swelling of the lymph nodes in his neck.
Dr. David E. Greenberg of the National Institute of Allergy and Infectious Diseases and his colleagues biopsied the lymph nodes, which they found to be extensively infected with the new organism, they reported Thursday in the journal Public Library of Science Pathogens.
Genetic analysis of the bacterium showed it to be a member of the Acetobacteraceae family, which includes several types of bacteria that are common in the environment and some that are used to make vinegar. No member of the family has previously been shown to cause human disease, however.
The team named the new bacterium \o7Granulobacter bethesdensis \f7in honor of the location of the NIH headquarters in Bethesda, Md. They have since found the bacterium in two other patients.