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Journal of Clinical Microbiology, July 2003, p. 3384-3386, Vol. 41, No. 7
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.7.3384-3386.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Low-Stringency Single-Specific-Primer PCR as a Tool for Detection of Mutations in the rpoB Gene of Rifampin-Resistant Mycobacterium tuberculosis
Wania S. Carvalho,1* Silvana Spindola de Miranda,2 Kátia M. Costa,3 José G.V.C. Araújo,3 Claudio J. Augusto,4 João B. Pesquero,5 Jorge L. Pesquero,3 and Maria A. Gomes3
Departamento de Farmácia Social, Faculdade de Farmácia,1
Faculdade de Medicina,2
and Instituto de Ciencias Biológicas,3
Fundação Ezequiel Dias, Belo Horizonte, Minas Gerais,4
Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil5
Received 4 September 2002/
Returned for modification 6 November 2002/
Accepted 23 March 2003

ABSTRACT
By the low-stringency single-specific-primer PCR technique,
a highly sensitive and rapid method for diagnosis of rifampin
resistance in
Mycobacterium tuberculosis was established. Seven
rifampin-resistant and five rifampin-susceptible specimens were
analyzed. Rifampin resistance was determined by MIC measurement.
A complex electrophoretic pattern consisting of many bands was
obtained for both susceptible and rifampin-resistant isolates.
The same pattern was obtained for all of the susceptible specimens,
but differences between resistant and susceptible isolates were
found. DNA sequencing showed that a particular mutation produces
a specific electrophoretic pattern.

TEXT
Tuberculosis has an extraordinary impact on the economies of
developing countries since the disease generally strikes individuals
in their prime working years. Resistance of
Mycobacterium tuberculosis to antituberculosis drugs is a conspicuously large public health
problem that has caused considerable distress in the involved
community. As important as the treatment of an infectious disease
is correct diagnosis of the resistance of the pathogen in the
patient to be treated. Incorrect treatment may turn the patient
into a source of dissemination of a resistant strain (
6). Rifampin
resistance is conferred by mutations in the
rpoB gene, which
encodes the beta subunit of RNA polymerase, an oligomeric enzyme
responsible for RNA synthesis (
13,
14). Resistance in approximately
95% of rifampin-resistant isolates is due to mutations in a
69-bp region of the
rpoB gene, corresponding to codons 511 to
533, making this a good target for molecular genotypic diagnostic
methods (
11). The mechanism of resistance in the remaining 5%
is still undetermined, with the exception of further mutations
at codons 381 (
8), 481 and 509 (
5), and 505 (
4) of the
rpoB gene. Point mutations within the 69-bp region of the
rpoB gene
involving codons Ser-531, His-526, Gly-513, and Asp-516 have
been shown to lead to high-level resistance in
Escherichia coli and
M. tuberculosis (
2,
9,
10,
12,
13). Current methods for
drug susceptibility testing of
M. tuberculosis in primary specimens
can take up to 8 weeks. The rapid detection of drug-resistant
M. tuberculosis in clinical specimens by molecular techniques
has been tried (
4,
5,
9,
10,
11,
12,
13) and may be a rational
and specific method to become popular in the future.
The low-stringency single-specific-primer PCR (LSSP-PCR) is an extremely simple technique that permits detection of single or multiple mutations in gene-sized DNA fragments (7). Two PCR steps are necessary. The first is a specific PCR (sPCR) to obtain the DNA template to be used in the second one, the LSSP-PCR, which uses low-stringency conditions and only one primer, usually one of the two primers used in the sPCR. In this study, we used the LSSP-PCR to detect mutations in the rpoB gene of M. tuberculosis isolates. We studied seven rifampin-resistant and five rifampin-susceptible M. tuberculosis isolates, of which four were from the sputum of patients in Minas Gerais, Brazil, with pulmonary tuberculosis and one was susceptible reference strain H37Rv. MIC determination (3) was performed for all of the M. tuberculosis isolates tested (0.06 to 64 µg/ml) (Table 1). The sPCR was carried out with primers RIF5 (GGCAACCGCCGCCTGCGTACG) and RIF3 (GCGGTACGGCGTTTCGATGAA). These primers were established to encompass the entire codified protein sequence (10) (GenBank accession number L05910). DNA was extracted from isolates with Trizol reagent (Life Technologies) in accordance with the protocol of the manufacturer. The reaction mixture consisted of 10 ng of purified mycobacterial DNA, 0.3 U of Taq DNA polymerase (Promega), 10 pmol of each primer, 200 µM deoxynucleoside triphosphates, 50 mM KCl, 1.5 mM MgCl2, and 0.1% Triton X-100 in 10 mM Tris-HCl buffer (pH 9.0) in a final volume of 10 µl. This reaction mixture was subjected to 30 cycles of amplification consisting of 1 min each of denaturation at 94°C, annealing at 70°C, and elongation at 72°C. Reaction products were run in a 1% agarose gel stained with ethidium bromide, and the specific 432-bp band was excised from the gel and purified with the QIAEX II gel extraction kit (Qiagen, Hilden, Germany). Primers RIF3 and RIF5 were tested in initial experiments for the LSSP step. Primer RIF3 was selected for use because it showed a major differentiation between resistance and susceptibility. The LSSP-PCR was carried out with a volume of 10 µl of 10 mM Tris-HCl (pH 9.0) containing 25 pmol of primer RIF3, 200 µM deoxynucleoside triphosphates, 1.0 U of Taq polymerase (Promega), 50 mM KCl, 1.5 mM MgCl2, 0.1% Triton X-100, and 15 ng of template DNA obtained in the sPCR and purified from agarose gel. Amplification was achieved with 39 cycles as previously described (1). Products were analyzed by polyacrylamide gel electrophoresis and stained with silver salts (Fig. 1). The same electrophoretic pattern was observed for all susceptible isolates, but differences between rifampin-resistant and -susceptible isolates were found. Alternatively, the 432-bp fragment was cloned for sequencing. No mutation was detected in the rpoB fragment from all of the sensitive isolates, whose DNA sequence was identical to that previously published for this fragment (10). DNA sequencing of resistant isolates WSJ225, IAS131, and EFP041 confirmed mutations within the 69-bp region in codon 526 or 531 (Fig. 2 and Table 2). The electrophoretic profiles of isolates IAS131 and EFP041 were very similar, and their DNA sequences were identical. It seems that a particular mutation gives a specific electrophoretic pattern.
Taking into account that the subunits of RNA polymerase are
conserved among prokaryotes (
2), our results, demonstrating
electrophoretic pattern differences between the DNAs of sensitive
and rifampin-resistant isolates extracted directly from sputum,
make LSSP-PCR a very promising tool for the diagnosis of antituberculosis
drug resistance. It seems that the electrophoretic pattern,
rather than band intensity, must be considered to define differences
between isolates. However, attention must also be paid to band
intensity since different fragments similar in electrophoretic
migration may occur. The results obtained in our study must
be validated with a great number of rifampin-resistant isolates.

ACKNOWLEDGMENTS
This work was supported by FAPEMIG and FAPESP.

FOOTNOTES
* Corresponding author. Mailing address: Departamento de Farmácia Social, Faculdade de Farmácia, Universidade Federal de Minas Gerais, Av. Olegário Maciel, 2360, 30180-112, Belo Horizonte, MG, Brazil. Phone: 55-31-3499-2942. Fax: 55-31-3339-7685. E-mail:
wscarv{at}icb.ufmg.br.


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Journal of Clinical Microbiology, July 2003, p. 3384-3386, Vol. 41, No. 7
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.7.3384-3386.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
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