Isoniazid-resistant Mycobacterium tuberculosis strains arising from mutations in two different regions of the katG gene.
OBJECTIVE
To analyze and compare the mutations in two different regions of the katG gene, which is responsible for isoniazid (INH) resistance.


METHODS
We analyzed 97 multidrug-resistant Mycobacterium tuberculosis strains isolated in cultures of sputum samples obtained from the Professor Hélio Fraga Referral Center, in Brasília, Brazil. Another 6 INH-sensitive strains did not present mutations and were included as controls. We used PCR to amplify two regions of the katG gene (GenBank accession no. U06258)-region 1, (from codon 1 to codon 119) and region 2 (from codon 267 to codon 504)-which were then sequenced in order to identify mutations.


RESULTS
Seven strains were resistant to INH and did not contain mutations in either region. Thirty strains carried mutations in region 1, which was characterized by a high number of deletions, especially at codon 4 (24 strains). Region 2 carried 83 point mutations, especially at codon 315, and there was a serine-to-threonine (AGC-to-ACC) substitution in 73 of those cases. The analysis of region 2 allowed INH resistance to be diagnosed in 81.4% of the strains. Nine strains had mutations exclusively in region 1, which allowed the proportion of INH-resistant strains identified to be increased to 90.6%.


CONCLUSIONS
The number of mutations at codon 315 was high, which is consistent with cases described in Brazil and in other countries, and the analysis of region 1 resulted in a 9.2% increase in the rate at which mutations were identified.
Siqueira
Helio Ribeiro de
HR
Faculdade de Ciências Médicas, Universidade do Estado do Rio de Janeiro, Rio de Janeiro, RJ, Brasil. drhelio@infolink.com.br
Freitas
Flávia Alvim Dutra de
FA
Oliveira
Denise Neves de
DN
Barreto
Angela Maria Werneck
AM
Dalcolmo
Margareth Pretti
MP
Albano
Rodolpho Mattos
RM
D000995:Antitubercular Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002374:Catalase / Q000235:genetics* / Q000378:metabolism; D003062:Codon / Q000235:genetics; D004269:DNA, Bacterial / Q000032:analysis; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D005798:Genes, Bacterial; D007538:Isoniazid / Q000494:pharmacology*; D009154:Mutation; D009169:Mycobacterium tuberculosis / Q000187:drug effects / Q000235:genetics*
D000995:Antitubercular Agents; D001426:Bacterial Proteins; D003062:Codon; D004269:DNA, Bacterial; D002374:Catalase; C480353:katG protein, Mycobacterium tuberculosis; D007538:Isoniazid