Resistance of Mycobacterium tuberculosis (MTB) to antituberculous drugs has been threatening the public-health
grossly. Recently, because of high-level of resistance to rifampicin in MTB, treatment is becoming impossible. In
this study, 127 rifampicin resistant and 33 rifampicin susceptible strains were randomly chosen from tuberculosis
culture-positive isolates, isolated in the laboratory of the Ataturk Chest Diseases and Chest Surgery Center in
Ankara, Turkey, over a 2-year period (1997 to 1998). Clinical samples collected from patients with suspected
tuberculosis were studied for acid-fast bacilli stain (AFBS) and cultured for detecting MTB. PCR was used to
amplify genetic loci associated with rifampicin resistance. The amplified 305-bp fragment of the rpoB gene was
applied to Heteroduplex assay for rapid detection of rifampicin resistance phenotype in MTB. The 127 rifampicinresistant
and 33 rifampicin-susceptible isolates, selected according to conventional culture method, were tested
again by PCR-Heteroduplex analysis. According to PCR-Heteroduplex analysis, 105 isolates of 160 M.
tuberculosis were rifampicin resistant, 55 strains were rifampicin susceptible. Of 127 rifampicin-resistant isolates
detected by conventional culture method, 101 had concordance with Heteroduplex analysis, whereas 26 isolates
did not. While 4 strains were detected as rifampicin susceptible by conventional culture technique, they were
rifampicin resistant by Heteroduplex analysis. It is thought that there might be a mutation out of fragment
amplified, in 26 strains which were not observed as rifampicin resistant by Heteroduplex analysis; or a mistake in
the result of resistance defined by classic culture method. In conclusion, however, PCR-Heteroduplex analysis is a
rapid and reliable method to detect rifampicin resistance, although it is a relatively expensive technique.
Key Words: M. tuberculosis, Rifampicin Resistance, PCR-Heteroduplex Analysis, Proportional Method.
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