Frequency of mutations in rpoB and codons 315 and 463 of katG in rifampin- and/or isoniazid-resistant Mycobacterium tuberculosis isolates from northeast Mexico

A total of 48 isoniazid (INH)- and rifampin (RIF)-resistant Mycobacterium tuberculosis isolates, 19 INH-resistant isolates, and 9 RIF-resistant isolates were randomly selected and tested for detecting mutations at codons 315 and 463 of katG by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), and/or for detecting mutations at a 69-bp region of the rpoB gene by the INNO-LiPA Rif TB assay. Of the 67 INH-resistant isolates tested, 36 (53.7%) showed the mutation at codon 315 of katG; however, none of them showed the mutation at codon 463. The majority of the RIF-resistant samples analyzed (49 of 57, 86.0%) reacted positive with one of the four R-type probes. The R5-pattern (S531L mutation) was the most frequently observed (31 of 57, 54.4%), followed by R4a-pattern (H526Y mutation) 13 isolates (22.8%), R4b-pattern (H526D mutation) 4 isolates (7.0%), and R2-pattern (D516V mutation) 1 isolate (1.8%). Overall, there was agreement between the line probe kit and phenotypic RIF-susceptibility test for 56 (98.2%) of 57 RIF-resistant isolates tested. These results show that the mutation analysis at codon 315 of katG could be used as a screening assay prior to standard susceptibility testing, whereas mutations in the rpoB gene could be used successfully as genetic markers to rapidly detect RIF-resistant M. tuberculosis clinical isolates from northeast Mexico.