Comparison of Rifampicin Drug Susceptibility Determined by Conventional Culture Method and Pcr-Heteroduplex Analysis in Mycobacterium Tuberculosis Strains

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.