The genus Mycobacterium encompasses more than hundred species including saprophytic and opportunistic or obligatory pathogenic species for humans and animals. The most important pathogens for humans are M. tuberculosis, M. leprae, and M. ulcerans while animals are more often affected by M. bovis, another member of the M. tuberculosis complex.

Tuberculosis is the leading killer among infectious diseases. It accounts for 1 in 4 preventable deaths among adults. The World Health Organization (WHO) estimates that worldwide each year there are about 8.5 million new cases of human tuberculosis and 2 million deaths from tuberculosis. Someone in the world is newly infected with tuberculosis every second, and it is estimated that one third of the world population is infected by M. tuberculosis.²⁷ Although leprosy is no longer considered a major health problem, M. leprae still accounts worldwide for about 500,000 to 750,000 cases each year in some endemic areas.²⁸ The geographical distribution of M. ulcerans, the causative agent of Buruli ulcer, is mainly limited to tropical and subsubtropical areas. This disease is most prevalent in Western Africa and most likely linked to the presence of stagnant water. In some of the rural areas of these countries the incidence of Buruli ulcer reaches or exceeds the incidence of tuberculosis.²⁹

Despite the availability of preventive and curative means for these mycobacterial diseases, there is still an urgent need for more sensitive and more rapid point-of-care diagnostic tests, new drugs to shorten the current treatment and to counter multi- and extensive-drug resistant tuberculosis, and a more effective vaccine than the currently used life-attenuated BCG vaccine. However, there is a dearth of good biological markers for the development of new diagnostic tests, the virulence mechanisms needed to develop more efficient vaccines for tuberculosis and Buruli ulcer and to better understand the pathogenesis of Buruli ulcer, and the drug targets for the development of new drugs. A bank of well-characterized mycobacterial strains can offer high-quality study material for fundamental research in these areas.

In addition, such a bank could offer reference material to evaluate new diagnostic tools and the anti-mycobacterial activity of new drugs and to provide quality assurance in identification and drug-susceptibility testing in clinical laboratories.

Despite their global importance for human and animal health, mycobacteria are underrepresented in culture collections worldwide in part because of the biosafety level required for the manipulation of airborne pathogens. There is no other collection of well-documented mycobacteria in the world as diverse and as large as the collection in the Mycobacteriology Unit of the Institute of Tropical Medicine, Antwerp, Belgium. Some 3000 to 5000 strains of these mycobacterial isolates will be selected and stored as freeze-dried materials in our appropriate L2 and L3 facilities. This selection of well-documented strains will be included in the public culture collection of mycobacteria.

M. tuberculosis-complex: Our collection of over 15,000 M. tuberculosis isolates with different drug susceptibility patterns is unique and comprises isolates from all the continents spanning from 1970 to date. They show various resistance profiles to the current first- and second-line drugs and have been characterized by phenotypic tests (Drug Susceptibility Testing and Minimal Inhibitory Concentrations) and/or genotypic tests (sequencing of relevant genes such as rpoB, katG, inhA and rrs). Most of the isolates have also been characterized by means of several DNA-fingerprinting techniques such as IS6110-based RFLP, spoligotyping and MIRU-VNTR typing. The unit also houses a public collection of wellcharacterized M. tuberculosis isolates for the WHO and Special Training for Research and Training in Tropical Diseases Research, Geneva, Switzerland. In addition, the unit also has a considerable number of M. bovis isolates from Belgium, Central Africa, and Ecuador.

M. ulcerans: We currently have over 500 M. ulcerans isolates in our collection. All of these isolates originate from cutaneous or bone lesions in humans except for one "unique" environmental isolate (00-1441) from an aquatic insect collected in a Buruli ulcer endemic region of Benin. The human isolates originate from all of the countries in which Buruli ulcer has been detected to date in Africa, Asia, Oceania and the Americas. We have isolates spanning from 1960 to date. All these isolates have been characterized using phenotypic and/or genotypic tests (IS2404-based PCR and MIRU-VNTR typing). Non-tuberculous mycobacteria (NTM): Our laboratory currently has over 10,000 isolates of NTM including most of the officially recognized species of the genus Mycobacterium. The isolates are of human, animal (mammals, fish, birds, amphibians, reptiles) and environmental (water, soil, dust, plants) origins and from all continents from 1970 to the present. All of these isolates have been characterized using phenotypic (biochemical tests, colony morphology, pigmentation, fatty acid analysis, etc.) and/or genotypic tests (analysis of the rrs gene or the 16S-23S spacer). Among these NTM, we have a unique collection of M. genavense and M. lepraemurium isolates, which are extremely difficult to culture in vitro.

Literature

27. WHO Report (2009) Global tuberculosis control - epidemiology, strategy, financing. WHO/HTM/TB/2009.411
28. WHO report (2008) Global leprosy situation. Weekly Epidemiological Record. N° 33, 15 August 2008
29. Silva MT, Portaels F, Pedrosa J (2009) Pathogenetic mechanisms of the intracellular parasite Mycobacterium ulcerans leading to Buruli ulcer. Lancet Infect. Dis. 9:699-710.

Contacts

Françoise Portaels

Leen Rigouts (lrigouts@itg.be)

Collection of Mycobacteria
Prince Leopold Institute of Tropical Medicine (ITM),
Mycobacteriology Unit,
Nationalestraat 155,
BE-2000 Antwerp.
Tel: + 32 3 247 65 51
Fax: + 32 3 247 66 33