Antimicrobial Agents and Chemotherapy, November 2004, p . 4293-4300, Vol . 48, No . 11

Rapid Direct Detection of Multiple Rifampin and Isoniazid Resistance Mutations in Mycobacterium tuberculosis in Respiratory Samples by Real-Time PCR

Mercedes Marín, Darío García de Viedma,^* María Jesús Ruíz-Serrano, and Emilio Bouza

Servicio de Microbiología y Enfermedades Infecciosas, Hospital General Universitario Gregorio Marañón, Madrid, Spain

Received 24 May 2004/ Returned for modification 9 July 2004/ Accepted 21 July 2004

Isoniazid (INH) and rifampin (RIF) are considered the mainstays of antituberculous treatment (1, 29) . The knowledge of the genetic basis of resistance to both drugs has provided molecular tools to rapidly detect the principal mutations conferring resistance to INH and RIF (2, 14, 16, 19) . Ninety-five percent of RIF resistance mutations in Mycobacterium tuberculosis are located in an 81-bp region of the rpoB gene (20) . The molecular basis of INH resistance is less well characterized, and mutations in several genes have been associated with it, although mutations in codon 315 of the katG gene are considered to be the most prevalent mutations encoding higher levels of resistance to INH (26) .

Despite the use of new liquid medium cultures, the isolation of M . tuberculosis is still time consuming and leads to delays in obtaining susceptibility patterns . Rapid methods to detect resistance are necessary to optimize antituberculous treatment and avoid the transmission of resistant strains . In the last few years, several molecular methods to detect resistance mutations in M . tuberculosis have been described (2, 6, 14); however, they are labor intensive and frequently require well-grown cultures . Recently, real-time PCR has made the rapid detection of resistance mutations from M . tuberculosis isolates possible (4, 5, 7, 22) . Nevertheless, little effort has been made to adapt these rapid methods to the detection of resistance directly from clinical samples (8, 10, 11, 13, 24, 27); therefore, genotypic susceptibility patterns still depend on culture .

Our aim is to adapt a real-time PCR design, recently developed in our laboratory (7), to assess resistance against RIF and INH in M . tuberculosis directly from clinical respiratory samples .

(This study was partially presented at the 13th European Congress of Clinical Microbiology and Infectious Diseases, Glasgow, United Kingdom, 10 to 13 May 2003 [P-636].)

The specimens were decontaminated by the N-acetyl-L-cysteine NaOH method (9) and conserved frozen at –70°C until use .

Spiked control specimens. An M . tuberculosis-negative sputum sample spiked with 10⁴ CFU of M . tuberculosis H37Rv/ml was used as a susceptible control .

To increase the variety of resistance mutations assayed, we obtained a set of 10 resistant controls after spiking a pool of M . tuberculosis-negative sputa with 10⁴ CFU of 10 different M . tuberculosis strains/ml encoding 11 different resistance mutations in rpoB (codons 511, 513, 514, 515, 516, 517, 526, 531, and 533) and three different substitutions in codon 315 of katG (see Table 2) . The resistance mutations assayed for the rpoB gene represent the different mutations detected in Spain up to the year 2002 because they are a selection of resistant strains compiled nationwide (provided by the Mycobacterium Reference Laboratory, Madrid, Spain) .

 
As specificity controls, we spiked a pool of M . tuberculosis-negative sputa with six mycobacteria (final concentration, 10⁴ CFU/ml) (M . bovis, M . avium, M . kansasii, M . gordonae, M . fortuitum, and M . chelonae) and eight nonmycobacterial species (Streptococcus pneumoniae, Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa, Nocardia asteroides, Haemophilus influenzae, and Klebsiella pneumoniae) .

Antibiotic susceptibility testing of isolates. The phenotypic susceptibility to INH and RIF was assayed by means of the SIRE method (Becton-Dickinson, Sparks, Md.), which is based on the agar proportion method .

DNA sequencing. In all cases, resistance mutations in rpoB and katG were determined by DNA sequencing with the same primers as those used for the real-time PCR . The amplicons obtained were purified by a commercial system (GFX PCR purification kit; Amersham Biosciences GmbH) . They were then sequenced by a PCR-based reaction with the Big Dye Terminator method (Applied Biosystems Inc.) according to the manufacturer's instructions and detected with an AbiPrism 3100 automatic DNA sequencer (Applied Biosystems Inc.) .

DNA extraction. Five hundred microliters of each decontaminated sample was centrifuged at 13,000 rpm with a Hettich Milkro 20 centrifuge for 15 min, and the supernatant was discarded . The pellet was resuspended in 50 µl of lysis solution (reagents 1 and 2 from an Accuprobe culture identification reagent kit; Gene Probe Inc., San Diego, Calif.) diluted 1:16 in fresh MGIT medium (Becton-Dickinson) and boiled for 5 min . Twenty-five microliters of sterile 106-µm glass beads (Sigma) was added, and the mixture was sonicated in a bath for 5 min . For sequencing purposes, the DNA was extracted from M . tuberculosis isolates in the same way .

Real-time PCR. The real-time PCR general design corresponded to that described previously (7) . Briefly, two pairs of fluorescence resonance energy transfer (FRET) probes (RPO1 and RPO2) labeled with different fluorophores were used to cover the rpoB core region (Fig . 1a) . RPO1 consisted of one probe labeled with fluorescein and the other labeled with LC Red 640 . RPO2 probes were labeled with fluorescein and LC Red 705 . Both probes were homologous to the wild-type sequence . Probes were detected by using two independent LC fluorescence channels (F2 for Red 640 and F3 for Red 705) . To detect mutations in katG, a pair of FRET probes (KAT) labeled with fluorescein and LC Red 640 was used (Fig . 1b) . The probes were homologous with the mutant sequence in codon 315 and detected in channel F2 . Each PCR run included a water negative control and a sputum sample spiked with the wild-type H37Rv control .

 
To adapt the real-time PCR to detect mutations directly on clinical samples, two major changes were included . First, the PCR was performed with three independent reactions to detect mutations in (i) rpoB with the RPO1 probes, (ii) rpoB with the RPO2 probes (Fig . 1a), and (iii) katG with KAT probes (Fig . 1b) . Second, an asymmetric PCR format was designed to increase the amount of target DNA which is complementary to the FRET probes .

(i) Primers and probes. The primers used were TR8 and TR9 (21) for the rpoB region and TB86 (21) and KatGR (5'-CTCCCACTCGTAGCCGTACA-3') for the katG gene . Probes were designed by TibMolBiol (DNA synthesis service; Roche Diagnostics . Berlin, Germany), and their sequences were as follows: for RPO1, 5'-CAGCTGAGCCAATTCATGGACC-fluorescein-3' and 5'-LC Red 640-AACACCCCGCTGTCGGG-phosphate-3'; for RPO2, 5'-ACAGACCGCCGGGCCCCAG-fluorescein-3' and 5'-LC Red 705-CGACAGTCGGCGCTTGTGGGT-phosphate-3'; and for katG probes, 5'-GACGCGATCACCACAGGCATCGAGG-fluorescein-3' and 5'-LC Red 640-CGTATGGACGAACACCCCGACGAAATGG-phosphate-3' .

(ii) Master mix. Two microliters of a 1:10 dilution of the DNA extract was used as a template for the PCR . The master mix was composed of 2 µl of LC FastStart plus deoxynucleotide mix (Roche Diagnostics), 10 pmol of each of the primers amplifying the strand which is complementary to each probe used (TR8 with RPO1, TR9 with RPO2, and KatGR with KAT), 2 pmol of the remaining primers, MgCl₂ (5 mM for rpoB and 4 mM for katG), 0.2 µM each Red-labeled probe, and 0.1 µM each fluorescein-labeled probe . The final reaction volume was 20 µl .

(iii) PCR conditions. Three independent reactions (with RPO1, RPO2, and KAT probes) were performed for each sample, and all of them shared the same PCR profile . Prior to PCR, a preincubation step of 95°C for 7 min was performed to activate the FastStart enzyme . The PCR consisted of 40 cycles with the following thermal sequence: 95°C for 10 s, 55°C for 8 s, and 72°C for 20 s . PCRs were performed in capillary tubes with a Light-Cycler real-time PCR instrument (Roche Diagnostics) .

(iv) Post-PCR analysis. PCR was followed by a melting step involving two sequential melting ramps, and the measurements were taken during the second step because it offered better definition in the melting curves (Fig . 2) . The first melting step consisted of 95°C for 5 s, 65°C (annealing temperature) for 30 s, 40°C for 0 s, and 95° for 0 s . This pattern was followed by 95°C for 5 s, 60°C for 30 s, 40°C for 0 s, and 95°C for 0 s . The rate of temperature increase was 0.2°C/s, and fluorescence was continuously acquired . Interpretation of melting data was done as previously described (7) . A mutation was suspected in the region covered by the probes when the deviations from the reference melting temperature (T_m) were higher than two times the standard deviation . Mutations in rpoB led to reductions in the reference T_m, and mutations in katG led to an increase in the reference T_m .

 
No result is given if a melting peak is not detected, which may be due to either amplification inhibition or undetectable amplification of an insufficient amount of template .

Analytical sensitivity. In order to assess the sensitivity of this method, 1 ml of a pool of culture-negative sputa was spiked with 10-fold dilutions of (i) M . tuberculosis H37Rv, (ii) rpoB mutants in codons 515 and 516 and 531 (TCGTTG), and (iii) a katG315 ACGACC mutant . Spiked sputa were cultured quantitatively in 7H11 Middlebrook agar . The amount of bacilli in each dilution was defined by determining the number of CFU in culture and by microscopic quantification of the number of bacilli by auramine staining performed with 50 µl of these controls . The spiked sputa were analyzed with a Light-Cycler instrument as described above for clinical samples .

DNA sequencing. The isolates which had been cultured from the specimens in analysis were sequenced . All samples containing RIF-resistant bacilli encoded mutations in rpoB (codons 514 and 515, 515 and 516, 526, and 531), and five samples harboring INH-resistant bacilli encoded mutations in codon 315 of katG (Table 1) . Four samples harboring INH-resistant bacilli were excluded from the study due to the lack of mutations in katG and thus, resistance in these strains could not be detected genotypically .

 
Real-time PCR detection of resistance in clinical samples. The reference T_m values for wild-type sequences were obtained by 10 repetitions of the assay using sputa spiked with the reference susceptibility control (M . tuberculosis H37Rv) . The average reference values for wild-type sequences were as follows: 67°C for RPO1, 64.88°C for RPO2, and 68.88°C for KAT (standard deviations, 0.1, 0.17, and 0.22°C, respectively) .

All clinical samples containing M . tuberculosis strains with a mutation in rpoB or katG were efficiently detected by this real-time PCR design . In all cases, T_m deviations (more than two times standard deviation) were detected with respect to the susceptible reference T_m (Table 1) .

All clinical samples containing RIF- or INH-susceptible strains showed a T_m within two times the standard deviation of the reference susceptible T_m .

Real-time PCR detection of resistance in spiked control specimens. In order to evaluate this real-time PCR design with a broader spectrum of resistance mutations, we tested 10 control specimens obtained by spiking a pool of negative sputa with different M . tuberculosis strains with known resistant mutations: for rpoB, nine different substitutions in eight independent codons, one deletion, and one double mutant in two codons were found; and for katG, three different substitutions in codon 315 (Table 2) .

Again, all samples harboring resistant strains were correctly detected by significant deviations from the reference wild-type T_m values (Table 2) .

Analytical sensitivity and specificity of real-time PCR. In order to assess the analytical sensitivity of the method, culture-negative sputa were spiked with serial dilutions of M . tuberculosis H37Rv and three different resistant strains . The amount of bacilli in each dilution was defined by determining the number of CFU in culture and by microscopic quantification of the number of bacilli . The test succeeded in detecting a bacterial load equivalent to 10³ CFU/ml (10 acid-fast bacilli/line) .

To determine whether the assay was specific for M . tuberculosis, we tested a set of negative sputa spiked with 14 nontuberculous mycobacteria and other bacterial genera . Only M . bovis (belonging to the M . tuberculosis complex) and M . avium (only with RPO1) led to a post-PCR melting fluorescent signal . Nevertheless, the T_m value obtained with M . avium was completely different from that obtained with M . tuberculosis (T_m = 53.7°C) .

In the present study, we tried to resolve this dual requirement of rapidity and polyvalent detection of a wide variety of resistance mutations in M . tuberculosis . A real-time PCR assay based on rapid cycle technology, recently developed by García de Viedma et al . (7) to detect multiple resistance mutations in a single reaction tube, was adapted to analyze M . tuberculosis resistance directly from clinical samples . This adaptation required (i) the real-time PCR design to be converted to an asymmetric format in order to preferentially amplify the DNA strands complementary to the probes and (ii) the three PCRs (with RPO1, RPO2, and KAT probes) to be performed in three independent reaction tubes .

In this sense, this design is methodologically similar to the design recently published by Ruiz et al . (17), which used FRET probes and rapid-cycle PCR to detect resistance to RIF and INH directly from clinical samples . Ruiz et al . (17) succeeded in detecting mutations from four patients with RIF-resistant isolates and seven patients with INH-resistant isolates . The present study is different in several ways . First, we evaluated a much wider variety of mutations encoding resistance (14 different mutations in 10 independent codons) . Secondly, in the study by Ruiz et al . (17), sequencing data were not available; therefore, neither the correlation of real-time PCR data with the genotypic "gold standard " nor the efficiency in detecting certain nucleotidic substitutions in different codons can be assessed . In this study, sequencing data are available for all 46 specimens, and thus, we can assure (i) 100% correlation with DNA sequencing and (ii) the efficiency of this system for detecting not only some specific prevalent mutations but also a huge variety of different mutations, some of them very rare . This result makes our system suitable for different geographic settings, as has been proved in a study done in Poland (18) in which part of this design has been applied, allowing the detection of mutations different from those tested here . In addition, in our method, the search of all rpoB and katG regions shares PCR conditions and allows all mutations to be detected in a single run, which makes for earlier availability of results . As a potential methodological limitation, it could be argued that this design does not detect INH-resistant mutations out of katG315 . Resistance to INH is less frequently found to be associated with mutations out of katG, and it is important to specify that isolates with mutations in katG315 show high-level resistance to INH, whereas isolates with mutations in loci other than katG are associated with low or intermediate levels of resistance to INH . In this context (7), in 92% of the resistant strains with a mutation in katG315, high MICs of INH (>3 µg/ml) were obtained, whereas most of the resistant strains with mutations other than those at katG315 had low MICs (<1 µg/ml) . Other authors (12; M . E . Verdú et al., Abstr . 12th Eur . Cong . Clin . Microbiol . Infect . Dis . 2002, abstr . P528) have found similar values, with most of the isolates encoding a katG315 mutation showing high levels of resistance to INH . It has recently been shown that among all the INH-resistant M . tuberculosis strains from Equatorial Guinea, none had mutations in katG and 80.5% had mutations in inhA (23) . All these resistant strains, with mutations mapping out of katG315, showed low levels of resistance to INH, and the patients responded to standard therapy . Additionally, katG315 mutations have also been found to be a marker for multidrug-resistant tuberculosis, and they are successfully transmitted within the population (26) . Taking all these data together, we believe that the inability of this real-time PCR design to detect INH-resistant mutations other than katG315 should not be cause for concern .

When searching for resistant mutations directly from clinical samples, the two main requirements an assay should be its ability to (i) guarantee specificity in the detection of mutations, considering that respiratory samples frequently include additional bacteria, and (ii) obtain high analytical sensitivity values .

We first tested whether amplification occurred when different respiratory pathogens were used as PCR templates . No amplification signal was found with 14 different non-M . tuberculosis pathogens . The only pathogens which led to an amplification signal were M . bovis and M . avium . It is not unexpected that M . bovis would lead to an amplification signal because it is included in the M . tuberculosis complex . With regard to M . avium, only the RPO1 probe produced a hybridization signal, and the T_m of the probe was easily differentiated from that obtained from M . tuberculosis (53.7 versus 67°C) . This finding rules out the possibility of a misinterpretation of the results .

Second, the analytical sensitivity of the assay was calculated to be 10³ CFU/ml (10 acid-fast bacilli/line) for the three regions assayed (RPO1, RPO2, and KAT), for both wild-type and mutant strains . In our laboratory, of the stain-positive samples obtained over 3 years, only three (17%) had a lower bacterial load . This finding means that this method would succeed in analyzing the susceptibility patterns of the majority of the stain-positive respiratory samples in this context . This method could be criticized for having used only stain-positive sputum samples . How useful this design is going to be in smear-negative specimens remains to be established . Few studies have data from stain-negative samples (10, 15, 27), and those studies are all based on traditional PCR and detect either rifampin or isoniazid resistance only, but never both . In our opinion, this limitation of analytical sensitivity should not be considered a weakness of this real-time PCR approach, especially if we consider the diagnostic context in which the susceptibility pattern of M . tuberculosis is usually requested . Generally, clinicians demand a rapid assessment of susceptibility when they receive the first laboratory evidence of M . tuberculosis infection, that is, microscopic observation of bacilli . Additionally, patients with stain-positive samples have a higher risk of causing transmission; therefore, the need for susceptibility patterns is particularly important in these cases . In all these situations, real-time PCR works properly, and requests for further assessment can be met satisfactorily . For stain-negative samples, it generally makes no sense to apply the real-time PCR, considering the low rate of positivity for M . tuberculosis in most mycobacterial laboratories in this context . In this case, M . tuberculosis was isolated in only 5.7% of all samples received from requests for mycobacteria culture .

The method described here combines an easy and short DNA extraction from clinical samples with a rapid, sensitive, and specific real-time PCR design . The complete assay, including analysis, enables us to obtain resistance results in 1[1/2] hours . To our knowledge, this assay is the first one based on real-time PCR that is able to detect, simultaneously and directly from clinical respiratory samples, numerous different mutations conferring resistance to RIF and those most frequently associated with high resistance to INH by using several FRET probes simultaneously in a single PCR run . The flexibility of real-time PCR assays to detect resistance mutations in different geographic settings cannot yet be answered, and international panels should be compiled and tested to answer this question .

The results obtained in this study lead us to propose this real-time PCR design as an adequate tool for the direct analysis of M . tuberculosis resistance in clinical samples . We are conscious that the introduction of real-time tools in the diagnostic laboratory requires specific installations and personnel to guarantee that the assay can be run upon receipt of the sample while traditional approaches to susceptibility tests are maintained, although this may not be the reality with regard to many laboratories . Efforts should be made, at least in specific reference laboratories, to adapt these new molecular procedures which allow the susceptibility pattern of M . tuberculosis to be obtained quickly, thus considerably reducing the time between diagnosis and initiation of individualized therapy .

The sequencer of Hospital Gregorio Marañon was acquired with a grant from Fondo de Investigaciones Sanitarias (01/3624) . This study was partially financed by grants from Comunidad de Madrid (08.2/0029.1/2001) and Fondo de Investigaciones Sanitarias (020882) . M . Marín has a contract from the Fondo de Investigaciones Sanitarias (FO1/48) .

We are indebted to Thomas O'Boyle for his revision of the English in the manuscript .

1. American Thoracic Society, Centers for Disease Control and Prevention, and Infectious Diseases Society of America. 2003 . Treatment of tuberculosis . Am . J . Respir . Crit . Care Med . 167:603-662.
2. Caws, M., and F . A . Drobniewski. 2001 . Molecular techniques in the diagnosis of Mycobacterium tuberculosis and the detection of drug resistance . Ann . N . Y . Acad . Sci . 953:138-145.
3. Edwards, K . J., L . A . Metherell, M . Yates, and N . A . Saunders. 2001 . Detection of rpoB mutations in Mycobacterium tuberculosis by biprobe analysis . J . Clin . Microbiol . 39:3350-3352.
4. El-Hajj, H . H., S . A . Marras, S . Tyagi, F . R . Kramer, and D . Alland. 2001 . Detection of rifampin resistance in Mycobacterium tuberculosis in a single tube with molecular beacons . J . Clin . Microbiol . 39:4131-4137.
5. Espasa, M . A., J . M . Gonzalez, F . Alcaide, J . Lonca, X . M . Manterola, E . Verdu, and P . Coll. 2002 . Use of real time PCR for direct detection in clinical samples of genetic polymorphisms causing resistance to isoniazid and rifampin in Mycobacterium tuberculosis . Clin . Microbiol . Infect . 8:O131.
6. Garcia de Viedma, D. 2003 . Rapid detection of resistance in Mycobacterium tuberculosis: a review discussing molecular approaches . Clin . Microbiol . Infect . 9:349-359.
7. García de Viedma, D., M . del Sol Díaz Infantes, F . Lasala, F . Chaves, L . Alcalá, and E . Bouza. 2002 . New real-time PCR able to detect in a single tube multiple rifampin resistance mutations and high-level isoniazid resistance mutations in Mycobacterium tuberculosis . J . Clin . Microbiol . 40:988-995.
8. Johansen, I . S., B . Lundgren, A . Sosnovskaja, and V . O . Thomsen. 2003 . Direct detection of multidrug-resistant M . tuberculosis in clinical specimens in low- and high-incidence countries by line probe assay . J . Clin . Microbiol . 41:4454-4456.
9. Kubica, G . P., W . E . Dye, M . L . Cohn, and G . Middlebrook. 1963 . Sputum digestion and decontamination with N-acetyl-L-cysteine-sodium hydroxide for culture of mycobacteria . Am . Rev . Respir . Dis . 87:775-779.
10. Leung, E . T.-Y., K.-M . Kam, A . Chiu, P.-L . Ho, W.-H . Seto, K.-Y . Yuen, and W.-C . Yam. 2003 . Detection of katG Ser315Thr substitution in respiratory specimens from patients with isoniazid-resistant M . tuberculosis using PCR-RFLP . J . Med . Microbiol . 52:999-1003.
11. Marttila, H . J., H . Soini, E . Vyshnevskaya, B . I . Vyshnevskiy, T . F . Otten, A . V . Vasilyef, et al. 1999 . Line probe assay in the rapid detection of rifampin-resistant Mycobacterium tuberculosis directly from clinical specimens . Scand . J . Infect . Dis . 31:269-273.
12. Marttila, H . J., H . Soini, E . Eerola, E . Vyshnevskaya, B . I . Vyshnevskiy, T . F . Otten, A . V . Vasilyef, and M . K . Viljanen. 1998 . A Ser315Thr substitution in KatG is predominant in genetically heterogeneous multidrug-resistant Mycobacterium tuberculosis isolates originating from the St . Petersburg area in Russia . Antimicrob . Agents Chemother . 42:2443-2445.
13. Mokrousov, I., T . Otten, M . Filipenko, A . Vyazovaya, E . Chrapov, E . Limeschenko, et al. 2002 . Detection of isoniazid-resistant Mycobacterium tuberculosis strains by a multiplex allele-specific PCR assay targeting katG codon 315 variation . J . Clin . Microbiol . 40:2509-2512.
14. Musser, J . M. 1995 . Antimicrobial agent resistance in mycobacteria: molecular genetic insights . Clin . Microbiol . Rev . 8:496-514.
15. Patnaik, M., K . Liegmann, and J . B . Peter. 2001 . Rapid detection of smear-negative Mycobacterium tuberculosis by PCR and sequencing for rifampin resistance with DNA extracted directly from slides . J . Clin . Microbiol . 39:51-52.
16. Rattan, A., A . Kalia, and N . Ahmad. 1998 . Multidrug-resistant Mycobacterium tuberculosis: molecular perspectives . Emerg . Infect . Dis . 4:195-209.
17. Ruiz, M . T., M . J . Torrez, A . C . Llanos, A . Arroyo, J . C . Palomares, and J . Aznar. 2004 . Direct detection of rifampin- and isoniazid-resistant Mycobacterium tuberculosis in auramine-rhodamine-positive sputum specimens by real-time PCR . J . Clin . Microbiol . 42:1585-1589.
18. Sajduda, A., A . Brzostek, M . Poplawska, E . Augustynowicz-Kopee, Z . Zwolska, S . Nieman, J . Dziadek, and D . Hillemann. 2004 . Molecular characterization of rifampin- and isoniazid-resistant Mycobacterium tuberculosis strains isolated in Poland . J . Clin . Microbiol . 42:2425-2431.
19. Telenti, A. 1997 . Genetics of drug resistance in tuberculosis . Clin . Chest Med . 18:55-64.
20. Telenti, A., P . Imboden, F . Marchesi, D . Lowrie, S . Cole, M . J . Colston, et al. 1993 . Detection of rifampicin-resistance mutations in Mycobacterium tuberculosis . Lancet 341:647-650.
21. Telenti, A., N . Honore, C . Bernasconi, J . March, A . Ortega, B . Heym, et al. 1997 . Genotypic assessment of isoniazid and rifampin resistance in Mycobacterium tuberculosis: a blind study at reference laboratory level . J . Clin . Microbiol . 35:719-723.
22. Torres, M . J., A . Criado, J . C . Palomares, and J . Aznar. 2000 . Use of real-time PCR and fluorimetry for rapid detection of rifampin and isoniazid resistance-associated mutations in Mycobacterium tuberculosis . J . Clin . Microbiol . 38:3194-3199.
23. Tudó, G, J . González, R . Obama, J . M . Rodriguez, J . R . Franco, M . Espasa, P . P . Simarro, G . Escaramis, C . Ascaso, A . Garcia, and M . T . Jimenez de Anta. 2004 . Study of resistance to anti-tuberculous drugs in five districts of Equatorial Guinea: rates, risk factors, genotyping of gene mutations and molecular epidemiology . Int . J . Tuberc . Lung Dis . 8:15-22.
24. Van Der Zanden, A . G., E . M . Te Koppele-Vije, N . Vijaya Bhanu, D . Van Soolingen, and L . M . Schouls. 2003 . Use of DNA extracts from Ziehl-Neelsen-stained slides for molecular detection of rifampin resistance and spoligotyping of Mycobacterium tuberculosis . J . Clin . Microbiol . 41:1101-1108.
25. van Doorn, H . R., E . C . J . Claas, K . E . Templeton, A . G . M . van der Zanden, A . K . Vije, M . D . Jong, J . Dankert, and E . J . Kuijper. 2003 . Detection of a point mutation associated with high-level isoniazid resistance in Mycobacterium tuberculosis by using real-time PCR technology with 3'-minor groove binder-DNA probes . J . Clin . Microbiol . 41:4630-4635.
26. van Soolingen, D., P . E . de Haas, H . R . van Doorn, E . Kuijper, H . Rinder, and M . W . Borgdorff, M . W. 2000 . Mutations at amino acid position 315 of the katG gene are associated with high-level resistance to isoniazid, other drug resistance, and successful transmission of Mycobacterium tuberculosis in The Netherlands . J . Infect . Dis . 182:1788-1790.
27. Whelen, A . C., T . A . Felmlee, J . M . Hunt, D . L . Williams, G . D . Roberts, L . Stockman, et al. 1995 . Direct genotypic detection of Mycobacterium tuberculosis rifampin resistance in clinical specimens by using single-tube heminested PCR . J . Clin . Microbiol . 33:556-561.
28. World Health Organization. 2000 . Anti-tuberculosis drug resistance in the world . Prevalence and trends . Report no . 2 . Publication W . H . O./CDS/TB/2000.278 . World Health Organization, Geneva, Switzerland.
29. World Health Organization. 2003 . Global Tuberculosis Programme . Treatment of tuberculosis: guidelines for national programmes . Publication W . H . O./CDS/TB/2003.13 . World Health Organization, Geneva, Switzerland.

Free Online Full-text Article

What is Food Microbiology?, What Is Nitrification?, What Is Antibiotic?, What Is Fermentation?, What Is Biofilter?, s, Microbe, i, Bacteriology, i, Microbiology, a, Microbes, i, Microorganism, s, Sepsis, r, Escherichia coli, n, S. cerevisiae, s, Eubacterium, r, Cell cultures, o, Antibiotics, n, Bacteriological, s, Vibriosis, n, Salmonella typhimurium, c, Clostridia, c, Thermophiles, c, Streptomycin, s, Streptococci, s, Antibiotics, n, Salmonella, i, Escherichia coli, e, Gram positive, o, Cell cultures, n, Bacteriological, i, Escherichia coli, a, Kluyveromyces




 

© 2005 Transgalactic Ltd (manufacturer of Bioscreen C software) | Privacy Statement | P.O. Box 1393, 00101 Helsinki, Finland, phone: +358 9 85172920, fax: +358 9 8749481, e-mail: microbiology@bionewsonline.com
 

Last modified: May 25, 2005