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Antimicrobial Agents and Chemotherapy, April 2000, p. 1075-1077, Vol. 44, No. 4
Institute for Medical Microbiology,
Regensburg, Germany
Received 26 July 1999/Returned for modification 23 September
1999/Accepted 10 January 2000
A clinical isolate of Helicobacter pylori that
developed resistance to rifabutin during therapy carried an
rpoB gene that retained a wild-type cluster region sequence
but had acquired a novel codon 149 (V149F) mutation. In transformation
experiments, the mutation was shown to confer high-level rifabutin
resistance. The equivalent mutation (V176F) was present in several
resistant isolates of Mycobacterium tuberculosis.
Rifabutin and other derivatives of
rifampin are inhibitory against Helicobacter pylori at very
low concentrations in vitro (1, 4). Triple therapy including
rifabutin, amoxicillin, and a proton pump inhibitor has been effective
in the eradication of H. pylori after failure of other
therapies and in spite of resistance to other antibiotics
(10). Resistance to rifampin and rifabutin is caused by
amino acid exchanges in the All resistant mutants of H. pylori ATCC 43504 selected in
vitro in a previous investigation (4) showed mutations in
the cluster region encompassing codons 525 to 545 and codon 586.
Here we describe a clinical isolate of H. pylori that
developed resistance during therapy. The patient was treated with
lanzoprazole and rifabutin, but amoxicillin was discontinued due to
intolerance. Isolates of H. pylori before (DR62a) and after
(DR62n) treatment were available for evaluation. Culture, storage,
E-test, agar dilution assay, PCR, and sequencing of the cluster region
were performed as described recently (4). Table
1 shows the primers for the amplification
and evaluation of large and small segments of the respective
rpoB regions. Sequencing was performed in both directions
(Perkin-Elmer Applied Biosystems).
0066-4804/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Mutations in the Beginning of the rpoB
Gene Can Induce Resistance to Rifamycins in both Helicobacter
pylori and Mycobacterium tuberculosis
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ABSTRACT
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TEXT
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subunit of the DNA-directed RNA
polymerase (RpoB). Mutations at codons 146, 507 to 533, 563 to 572, and
687 of the rpoB gene in Escherichia coli
(11) or at codons 507 to 533 (cluster region) in
Mycobacterium tuberculosis (8, 9) have been shown
to induce resistance.
TABLE 1.
PCR primers for amplification and sequencing of the
respective H. pylori and M. tuberculosis
rpoB segments
DR62n was resistant to rifampin (E-test, MIC of >256 µg/ml) and
rifabutin but, in contrast to previous findings (4), showed no difference from the published wild-type sequence (14) in the cluster region. The MICs of rifabutin for H. pylori
DR62a and DR62n were 0.002 and 8 µg/ml, respectively (Table
2). Both strains yielded homologous
patterns when typed by arbitrarily primed PCR (2;
unpublished work). Amplification and sequencing of DR62n
rpoB (rifabutin resistant) from bp 387 to bp 916 revealed a
codon exchange, GTC
TTC (V149F). DR62a (rifabutin susceptible) showed
wild-type sequence in both the V149 region and the cluster region.
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In order to confirm that the amino acid mutation V149F is responsible for high-level resistance, large fragments of the rpoB gene (bp 54 to 916 harboring codon 149 and bp 1271 to 2106 harboring the cluster region) from DR62n and DR62a were amplified and sequenced. The amino acid mutation V149F was the only difference between DR62n and DR62a or the published wild-type sequence (14). All fragments were transformed into a competent, rifabutin-susceptible strain, H. pylori 2802A. Transformation of H. pylori 2802A was done, using a dense suspension of a fresh culture adjusted to a McFarland standard of >4 in 1 ml at an optical density value at 550 nm (OD550) of 10, diluted to an OD550 value of 0.2 in brucella broth with 8% fetal calf serum. One milliter of a suspension with an OD550 value of 0.2 (in a 24-well plate) was incubated at 36°C with 3 to 5% CO2 for 6 h. At 0, 2, and 4 h, 3 to 10 µl of a PCR product (1 to 3 µg of DNA) was added. Cells were cultured on Wilkins-Chalgren agar containing rifabutin (0.03 µg/ml) under microaerophilic conditions for 3 to 5 days. Single colonies were picked and grown on selective agar for MIC determination, storage, DNA amplification, and sequencing.
Repeated transformation of H. pylori 2802A with PCR products harboring the V149F mutation (bp 54 to 916 from DR62n rpoB) generated 105 to 106 CFU/well (2802A-R) showing the same level of resistance as seen in the donor strain (Table 2). Transformation with PCR products of the wild-type 5' region (bp 54 to 916) or cluster region (bp 1371 to 2106) of H. pylori rpoB generated fewer than five resistant colonies per well.
Positive controls for the cluster region (e.g., Q527R) were amplified from the DNA of rifabutin-resistant H. pylori ATCC 43504 variants (4) and generated 105 to 106 CFU/well (data not shown).
After we had the confirmation of a newly described mutation outside the cluster region conferring high-level resistance in H. pylori, we wondered whether this arrangement might also occur in M. tuberculosis. PCR-based systems for the detection of mutations in the cluster region are of outstanding importance for the determination of rifampin susceptibility of slow-growing organisms like M. tuberculosis but sometimes fail to match with a resistant phenotype. Reported failure rates range from 3 to 6% (3, 5, 7, 9, 13, 16, 17). DNA samples of six M. tuberculosis isolates from Japan for which MICs of rifampin were elevated but with wild-type sequence in the rpoB cluster region were provided by the authors of reference 17.
Primers for PCR and sequencing are shown in Table 1. Three out of six
samples showed the mutation GTC
TTC (V176F), consistent with our
findings in DR62n. The amino acid changes detected are shown in Table 2
and mapped in Fig. 1. There is no report
in the literature so far of a mutation in this region in mycobacteria.
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Rudi Rossau et al. (Innogenetics) recently presented data at a meeting (R. Rossau, W. Mus, G. Jannes, K. de Smet, H. van Heuverswijn, H. Traore, and F. Portaels, 20th Annu. Congr. Eur. Soc. Mycobacteriol., abstr. OC27, p. 44, 1999) which are in strong agreement with ours and emphasize the importance of our findings. They investigated 203 resistant M. tuberculosis isolates, finding discrepant results in four isolates. Three out of four samples showed the mutation V176F, induced by the same base exchange. Their collection contained no isolates from Japan. However, no comparable mutation in eight resistant M. tuberculosis strains with the wild-type cluster region was found by Telenti et al. (8; A. Telenti, personal communication; no MIC given).
The amino acid mutation V146F conferring high-level resistance in E. coli was first observed by Lisitsyn et al. in 1984 (6) and verified by Severinov et al. (12) by site-directed mutagenesis (Fig. 1). Recently, three mutations associated with resistance were described for a Rickettsia typhi isolate (15). Mutations were observed at codons 151 (F151L), 201, and 271. Codon 151 is located next to the region which has been shown to confer resistance and is possibly the one responsible for the resistant phenotype. Out of six M. tuberculosis isolates, three with the higher level of resistance to rifampin (8 to 32 µg/ml) carried the V176F mutation, while the low-level resistance (1 to 4 µg/ml) remains unexplained.
Mutations in the 5' region of the rpoB gene inducing rifamycin resistance in H. pylori and possibly in M. tuberculosis have not been sufficiently examined. Resistance can be caused by a single base exchange outside the cluster region. This should be considered in future developments of molecular biology-based testing for mycobacteria.
The high homology of this region on the amino acid level (Fig. 1) indicates that there might be mutations conferring resistance in other species like Legionella pneumophila or Staphylococcus aureus as well.
Nucleotide sequence accession numbers. The relevant sequence fragments of M. tuberculosis strain 84 and H. pylori DR62n have been deposited in the GenBank database under accession no. AF 177294 and AF 177295, respectively.
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ACKNOWLEDGMENTS |
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The DNA samples of resistant M. tuberculosis isolates were kindly provided by Shigeru Kohno, Nagasaki University, Nagasaki, Japan. H. Bock, Frankfurt, Germany, provided the biopsy specimens from the patient before and after H. pylori eradication therapy. We thank Regine Birngruber for excellent technical assistance.
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FOOTNOTES |
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* Corresponding author. Mailing address: Institut für Medizinische Mikrobiologie, Uniklinik Regensburg, D-93053, Regensburg, Germany. Phone: 49 941 944-6414. Fax: 49 941 944-6402. E-mail: Markus.Heep{at}klinik.uni-regensburg.de.
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