GENOTYPIC ASSESSMENT OF ISONIAZID AND RIFAMPIN RESISTANCE IN MYCOBACTERIUM-TUBERCULOSIS - A BLIND-STUDY AT REFERENCE LABORATORY LEVEL

Progress in understanding the basis of resistance to isoniazid (INH) a nd rifampin (RMP) has allowed molecular tests for the detection of dru g-resistant tuberculosis to be developed, Consecutive isolates (n = 95 ) of Mycobacterium tuberculosis, from a Spanish reference laboratory i nvestigating outbreaks of multidrug-resistant tuberculosis, were coded and sent to two external laboratories for genotypic analysis of INH a nd RMP resistance by PCR-single-strand conformation polymorphism (SSCP ) analysis of specific regions of four genes: part of the coding seque nce of katG and the promoter regions of inhA and ahpC for INH and the RMP resistance region of rpoB, After correction for the presence of ou tbreak strains and multiple isolates from single patients, RMP resista nce was detected successfully by PCR-SSCP in >96% of the RMP-resistant strains, PCR-SSCP had a sensitivity of 87% for INH resistance detecti on, and mutations in katG, inhA, katG-inhA, ahpC, and kaG-ahpC were id entified in 36.8, 31.6, 2.6, 13.2, and 2.6%, respectively, of the uniq ue strains, Specificity was 100%, Molecular detection of resistance to the two main antituberculous drugs, INH and RMP, can be accomplished accurately by using a strategy which limits analysis to four genetic r egions, This may allow the expedient analysis of drug resistance by re ference laboratories.