| Popis: |
In a recent paper by Rao et al. (3), the easy and rapid mycobacterial interspersed repetitive unit (MIRU) locus 26 PCR assay was found to be 100% specific and sensitive for the discrimination of the Beijing genotype Mycobacterium tuberculosis strains from the non-Beijing strains based on the assumption that all Beijing strains have seven copies and non-Beijing strains have fewer or more than seven MIRU copies at locus 26. Unfortunately, however, it is known that not all Beijing isolates carry seven MIRU copies at locus 26 (2, 4). Particularly, in some geographic regions, such as the countries of the former USSR, Beijing genotype strains with fewer than seven MIRU copies at locus 26 are in striking predominance over strains with seven copies (2). Recently, we showed that Beijing genotype strains recovered in Istanbul were carried over from the countries of the former USSR, and of the 46 Beijing genotype strains, 37 strains were found to have fewer than seven MIRU copies at locus 26 (1). After having performed spoligotyping and MIRU typing for more than 2,000 M. tuberculosis strains in Istanbul, we also encountered some non-Beijing strains which had seven repeats at MIRU locus 26. These non-Beijing strains with seven repeats at locus 26 were of the T1, LAM-9, Haarlem 1, CAS 1, 703740004000760, 703777740003371, and 777777774760771 spoligotypes. In conclusion, the sensitivity and specificity of the MIRU locus 26 PCR assay may not be 100% as was found in this study (3), and this assay seems to be far from reliable as a screening tool to identify and discriminate Beijing genotype strains from non-Beijing strains, since there are Beijing genotype strains with fewer or more than seven repeats at locus 26 and, conversely, non-Beijing strains with seven repeats. |
