Molecular genetic diagnosis of mycobacteria

(modified from: V. Allerheiligen, Management&Krankenhaus 21(10), 38 (2002))

General

Mycobacteria are clinically important since they cause two scourges of mankind: leprosy and tuberculosis. Whereas leprosy is now relatively unimportant in developed countries, tuberculosis diseases and other mycobacterioses have now started to increase again in recent years. This is due to the increasing mobility of humans and to the increasing number of immunosuppressed patients which are particularly susceptible to atypical mycobacterial infections. Another reason is that the disease is now easier to diagnose. Despite the improved methods of diagnosis and treatment, 3 million people still die anually from tuberculosis!

Figure: Patient with tuberculosis

Microscopy and culture

Since the discovery of Mycobacterium tuberculosis as the pathogen of consumption by Robert Koch at the end of the 19th Century, major advances have been made in the diagnosis and treatment of tuberculosis. Nevertheless the diagnosis of tuberculosis remains complicated and laborious. Thus although the direct detection of mycobacteria in patient specimens by staining and subsequent microscopy is a rapid and cheap method, it requires a high bacterial count in the specimen for a reliable result.

Figure: Auramine staining

In addition to the lack of sensitivity, a differentiation of the microorganisms is hardly possible using microscopy. Hence in routine diagnostics multiple culture of mycobacteria in special liquid and solid media is still the gold standard for detecting mycobacteria in the various specimen materials. Culture allows isolation rates of more than 90 %. Cultures that have grown indicate the presence of mycobacteria and additionally enable a differentiation of the mycobacterial species when the findings are positive. In this connection it is important to rapidly and reliably exclude an infection with M. tuberculosis. However, it can take up to 6-8 weeks before the mycobacteria, which in some cases grow very slowly allow a reliable evaluation of the culture. Hence an early and specific treatment of the patients is not possible. Moreover it is very difficult to biochemically differentiate atypical mycobacteria and the specificity is very low. However, molecular biology is now becoming more important in the diagnosis of mycobacteria. It supports the culture tests either by serving as a direct test on the specimens which gives rapid results or by enabling a rapid and unequivocal species differentiation from culture material. Nucleic acid based methods have largely displaced the classical methods. 

Figure: M. avium, a very prevalent atypical mycobacterium

Molecular biological diagnostics

Molecular biology increases the number of method-independent test procedures and thus increases the diagnostic reliability. An extremely desirable effect! A rapid detection and a rapid differentiation enable a rapid start to treatment which contributes to a reduction of the treatment and secondary costs. Since tuberculosis is a reportable disease, the high diagnostic reliability offered by the additional molecular genetic tests avoids unnecessary difficulties. Moreover, the molecular genetic tests give the testing laboratory considerable time advantages in the differentiation enabling a more rapid initiation of resistance tests and specific treatment. 
The GenoType® Mycobacterial series offered by Hain Lifescience GmbH consists of two products which can be used to carry out molecular genetic mycobacterial tests including their differentiation in a cost-effective and reliable manner. Whereas older test systems only allow a differentiation of a limited number of individual species in an exclusion procedure, the „GenoType® Mycobacterium“ test not only enables a differentitation of the M. tuberculosis complex but also simultaneously the 12 other mycobacterial species from the culture without time-consuming and costly parallel testing. The „GenoType® MTBC“ test even allows a differentiation between the species of the M. tuberculosis complex. Both tests are designed to meet the requirements of customers and have proven to be extremely economical in routine use. Independent studies of mycobacterial reference centres in Spain, Finland and Germany have confirmed the high quality of the CE labelled tests. The manufacturer's  ISO 9001:2000/EN 46001 certification demonstrates the implementation of a modern quality management system and thus guarantees the highest standards. The GenoType® tests can be fully automated if required.

Summary

Molecular genetic test methods like the mycobacterial tests from the GenoType®-Series (Hain Lifescience GmbH, Nehren) are an indispensable tool for the detection and differentiation of mycobacteria from cultures. Both tests are characterized by maximum specificity and sensitivity. Processing of the two tests is carried out in an identical manner and does not require complex apparatus; it is neither time-consuming nor labour-intensive. A reliable and rapid diagnosis is crucial for a timely and specific start to treatment and thus has clear cost advantages. The „GenoType® Mycobacteria Direct“ test which will be launched in Spring even allows the molecular diagnosis of M. tuberculosis and five other clinically relevant atypical bacteria directly from patient material. This test will also be distinguished by simple handling and instrumentation. The simple and rapid procedures and the option of automation thus make the mycobacteria tests from Hain Lifescience an ideal partner in mycobacterial diagnostics.