[Standardization of laboratory tests for tuberculosis and their proficiency testing].

Abstract

Explanations of proper collection procedures are imperative for accurate laboratory analysis. The quality of specimens collected and the proper transport of those specimens to the laboratory are critical to successful isolation of etiological agents. Most mycobacteria grow at a relatively slow rate. Therefore, the acid-fast smear plays an important role in the early diagnosis of mycobacterial infection. There are several methods of determining the acid-fast nature of an organism. In the carbolfuchsin procedures (Ziehl-Neelsen, Kinyoun), acid-fast organisms appear red, and in the fluorochrome procedures (auramine O, auramine-rhodamine, acridine orange), the acid-fast organisms fluoresce yellow to orange. Fluorochrome-stained slides may be directly restained with any of the carbolfuchsin staining procedures. This may be done to confirm a positive fluorochrome slide and to study organism morphology. In the last 10 years, there were many advances in the culture examinations of mycobacteria. The newly developed Mycobacteria Growth Indicator Tube (MGIT), BacT/Alert, ESP Myco, MB Redox and KRD "Nichi B", biphasic Septi-Chek AFB and Myco-Acid, and radiometric BACTEC 460TB systems based on liquid media, proved to be significantly better than the egg-based solid media for the isolation of mycobacteria from clinical specimens. In addition to liquid-based medium, agar (Middlebrook 7H10 or 7H11)- or egg (Ogawa or Löwenstein-Jensen)-based media should be used in the primary isolation of mycobacteria. To identify mycobacteria, conventional biochemical tests are traditionally used. Key test can be used to identify species, or further preliminary grouping may be used. Other approaches to identifying some species of mycobacteria are available. They include niacin accumulation, p-nitrobenzoic acid and p-nitro-alpha-acetylamino-beta-hydroxypropiophenone tests for discrimination of the Mycobacterium tuberculosis complex from mycobacteria other than M. tuberculosis (MOTT); DNA probe methods for identification or confirmation of the M. tuberculosis complex, M. avium complex, M. kansasii, and M. gordonae; DNA-DNA hybridization method for identification of 22 Mycobacterium species; and gas-liquid chromatography or high performance liquid chromatography analyses for recognizing the patterns of the mycobacterial cell wall fatty acids or mycolic acids. The advantages of the last four methods are that they are capable of providing definitive identification within 2 to 5 h after adequate growth. Capilia TB is the newly developed immunochromatographic assay for rapid discrimination between the M. tuberculosis complex and MOTT bacilli. The kit can be easily used for rapid identification of the M. tuberculosis complex in combination with the culture systems based on liquid media. In addition, Capilia TB could correctly detect the M. tuberculosis complex from mixed cultures with the M. tuberculosis complex and MOTT bacilli. The WHO/IUATLD supranational reference laboratory (SRL) network was created in 1994, to ascertain the accuracy of the susceptibility test methods used in different laboratories across the world, and to allow comparability of the surveillance data gathered in countries participating in the Global Project on Anti-tuberculosis Drug Resistance Surveillance. Today, the network has evolved and 23 SRLs actively participate. Results of five rounds of proficiency testing in the SRL network suggest that performance of the network has improved substantially through the years. This progress has been particularly evident for streptomycin and ethambutol sensitivity, which was very low in the first rounds of proficiency testing. In 1998 sensitivity for these two drugs was higher than 95%. For isoniazid and rifampin, sensitivity has been consistently high since the beginning of the Global Project. This indeed reflects the enhanced efforts made by the SRLs to improve their individual performance.