NEWS & EVENTS

NEWS ARCHIVE | EDUCATIONAL RESOURCES

MYCOBACTERIA

In much of the world, infections caused by mycobacteria, particularly M. tuberculosis, still represent the leading cause of death from an infectious agent. With public health measures and generally better health, the number of cases of tuberculosis (TB) in the US decreased after 1900, until a reversal of this trend in the mid-80's, after which the incidence of TB again peaked in 1992. Though the number of cases is again declining in the US, TB continues to be a health problem worldwide, with drug-resistance of the organisms becoming a major concern (currently, 15% of US cases). In the US, factors supporting the continued presence of TB include HIV infection, homelessness, migrant workers, immigrants, nursing home/elderly patients, and prison populations.

Clinically, mycobacteria can infect most of the tissues of the body, but most human infections are of the lung. M. tuberculosis is the species most responsible for pulmonary TB in the US. However, occasionally (1%) some are caused by M. bovis (usually gastrointestinal infections). There are several other species (M. avium, M. intracellulare, and M. kansasii) termed "atypical mycobacteria", that also produce a generally milder form of chronic lung disease.

Mycobacteria are aerobic bacilli (hence their propensity for the lungs) that have a peculiar staining characteristic (acid-fast) and grow very slowly in laboratory cultures (weeks to months). This latter fact has greatly delayed the definitive diagnosis of mycobacterial infections until recently.

Physicians Reference Laboratory is now using an elegant new technology to rapidly identify and report mycobacterial infections, usually within 4-7 days. This new technique is based upon the utilization of oxygen by the growing mycobacteria, while other bacterial growth is inhibited. Because some mycobacteria grow extremely slowly, a negative report will not be issued until 6 weeks.

Kenneth C. Cummings, MD
Chief, Clinical Pathology
October 16, 2001