NIH News Advisory
National Institute of
Allergy and Infectious Diseases

Wednesday, March 15, 2000
Sam Perdue
(301) 402-1663

NIAID-Supported Scientists Decipher Genetic Code for "Chlamydia" Species:
Implications for Diseases from STDs to Atherosclerosis

Researchers supported by the National Institute of Allergy and Infectious Diseases (NIAID) have determined the complete genetic blueprints for two unusual bacteria that cause a number of common diseases. One of these bacteria also has been implicated in chronic disorders such as heart disease, an active area of ongoing research.

In the March 15 issue of Nucleic Acids Research, scientists from the United States and Canada report the complete DNA sequences of strains of Chlamydia trachomatis and C. pneumoniae1. Both species live inside host cells, a property that distinguishes them from most other bacteria, but they differ from each other in the diseases they cause. C. trachomatis causes trachoma, a preventable form of blindness in infants, and infections of the genital tract in adults. C. pneumoniae causes pneumonia, bronchitis and, more rarely, sore throats and sinus infections. This microbe has also received increased attention because of reports suggesting it might be linked to cardiovascular disease. Limited studies also suggest a possible role for C. pneumoniae in other chronic disorders such as Alzheimer's disease, arthritis and asthma, but more research is needed in these areas.

Two previous studies, one funded by NIAID, uncovered the first genetic blueprints for one strain each of C. trachomatis and C. pneumoniae.(2,3) By comparing their genetic organization, researchers have determined which genes are likely to be important for the different disease-causing properties of these two species.

The latest DNA sequences provide genetic information on two additional strains of the bacteria, one of each species. Because two strains of the same species — C. pneumoniae, for example - can differ in their ability to cause illness, such a comparison is critical to identifying the strain-specific genes responsible for different types of disease.

As scientists further examine the connection between C. pneumoniae and chronic illnesses, this new sequence information may help in developing assays for detecting the presence of the microbe or its components in individuals and in establishing whether there is a connection between C. pneumoniae infection and the development of heart disease.

The recent genome sequencing projects were directed by Claire M. Fraser, Ph.D., of The Institute for Genomic Research in Rockville, Maryland, with researchers from the University of British Columbia Centre for Disease Control and the University of Manitoba. The previously reported Chlamydia sequence research was directed by Richard S. Stephens, Ph.D., of the University of California, Berkeley, in collaboration with researchers from the University of California at San Francisco, Stanford University and the National Institutes of Health.

Press releases, fact sheets and other NIAID-related materials are available on the NIAID Web site at

The National Institute of Allergy and Infectious Diseases is a component of the National Institutes of Health, U.S. Department of Health and Human Services.

1. TD Read et al. Genome sequences of Chlamydia trachomatis MoPn and Chlamydia pneumoniae AR39. Nucleic Acids Res 28:1397-1406 (2000).

2. RS Stephens et al. Genome sequence of an obligate intracellular pathogen of humans: Chlamydia trachomatis. Science 282:754-59 (1998).

3. S Kalman et al. Comparative genomes of Chlamydia pneumoniae and C. trachomatis. Nature Genet 21:385-89 (1999).