Rifampin and isoniazid resistance associated mutations in Mycobacterium tuberculosis clinical isolates in Seville, Spain

The susceptibility phenotypes of 964 clinical isolates of Mycobacterium tuberculosis were studied over a 7-year period in Seville, Spain. Thirty-eight (3.9%) strains were rifampin (RMP) resistant, 79 (8.2%) were isoniazid (INH) resistant and 22 (2.3%) were resistant to at least both antimicrobials (multidrug-resistant, MDR). We studied the mechanisms of resistance to these drugs in 94 resistant clinical isolates of M. tuberculosis using three molecular methods: 1) PCR-single strand conformation polymorphism (SSCP) analysis, 2) RFLP analysis using B1/B2 primers, and 3) sequence analysis. Five different mutations were detected in the rpoB gene: Ser.(531)-->Leu (72.3%), His(526)-->Asp (12.8%), Asn(518)-->Ser (2.1%), Gln(513)-->Leu (2.1%) and a nine-nucleotide deletion (2.1%). In the case of resistance to INH, four different mutations in the katG gene were detected, Ser(315)-->Thr (58.0%), Ser(315)-->Leu (2.9%), partial deletion (5.8%) and Ile(304)-->Val (1.4%), while in the inhA regulatory region the only mutation was the nucleotide substitution C209T (4.3%). No mutation was found in the ahpC promoter.