Frequency and implications of pyrazinamide resistance in managing previously treated tuberculosis patients.

OBJECTIVE: To determine the extent of pyrazinamide (PZA) resistance in isolates from previously treated patients from the Western Cape, South Africa. DESIGN: Drug-resistant isolates, isolates resistant to one or more drugs other than PZA (PZA resistance is not routinely determined) (n = 127), and drug-susceptible (n = 47) clinical isolates of Mycobacterium tuberculosis from previously treated patients from the Western Cape were phenotypically (BACTEC MGIT 960) and genotypically (pncA gene sequencing) analysed for PZA resistance. RESULTS: MGIT analysis found that 68 of the 127 drug-resistant isolates were PZA-resistant. Nearly all (63/68) PZA-resistant isolates had diverse nucleotide changes scattered throughout the pncA gene, and five PZA-resistant isolates had no pncA mutations. Of the 47 phenotypically susceptible isolates, 46 were susceptible to PZA, while one isolate was PZA-monoresistant (OR = 53.0, 95% CI = 7.1-396.5). A pncA polymorphism (Thr114Met) that did not confer PZA resistance was also identified. PZA resistance was strongly associated with multidrug-resistant tuberculosis (MDR-TB). CONCLUSION: An alarmingly high proportion of South African drug-resistant M. tuberculosis isolates are PZA-resistant, indicating that PZA should not be relied upon in managing patients with MDR-TB in the Western Cape. A method for the rapid detection of PZA resistance would be beneficial in managing patients with suspected drug resistance.     

The paradox of pyrazinamide: an update on the molecular mechanisms of pyrazinamide resistance in Mycobacteria

Pyrazinamide (PZA) is an important front line anti-tuberculosis drug because of its sterilizing activity against semi-dormant tubercle bacilli. In spite of its remarkable role in shortening the treatment duration from 9 months to 6 months when used in combination with Rifampicin and Isoniazid, PZA remains a difficult paradox because of its incompletely understood mode of action and mechanism of resistance. PZA is a nicotinamide analog prodrug which is converted into the active bactericidal form pyrazinoic acid by the bacterial enzyme pyrazinamidase (PZase). PZA does not appear to have a specific cellular target and instead, exerts its bactericidal effect by disrupting the membrane energetics and acidification of cytoplasm. Majority (72-97%) of PZA-resistant isolates of M. tuberculosis exhibit mutations in their pncA gene or upstream area leading to loss of PZase activity. A wide diversity of pncA mutations scattered along the entire length of pncA gene is unique to PZA resistance. However, PZA resistant isolates with normal PZase activity and wild type pncA sequences have also been reported in several studies which indicate that alternate mechanisms of PZA resistance exist. Investigations into these mechanisms would be useful in developing alternative diagnostic/therapeutic measures. This review presents the update of various mechanisms of PZA resistance in different mycobacteria with special emphasis on mode of action of PZA and mechanisms of resistance in Mycobacterium tuberculosis.     

Characterization of pyrazinamide and ofloxacin resistance among drug resistant Mycobacterium tuberculosis isolates from Singapore.

OBJECTIVES: To evaluate rapid molecular approaches for the detection of pyrazinamide (PZA) and ofloxacin resistance, by screening 100 known drug-resistant Mycobacterium tuberculosis isolates. METHODS: Mycobacterium tuberculosis isolates were tested for phenotypic resistance to pyrazinamide and ofloxacin using the BACTEC 460 radiometric method and the E-test, respectively. Mutation screening was done by amplifying the pncA, gyrA, and gyrB genes by the polymerase chain reaction (PCR) and direct automated sequencing. RESULTS: Twelve isolates were PZA-resistant and 8 of 12 (66.7%) isolates had missense mutations or deletions at the pncA gene, suggesting that mutation or deletion at the pncA gene is the major molecular mechanism of PZA resistance among the Singaporean isolates. Using the E-test, 48 isolates were resistant to ofloxacin, with minimum inhibitory concentrations of 4 microg/mL or higher. No mutations were observed at the quinolone resistance-determining region (QRDR) of gyrA in all isolates. At the QRDR of gyrB, mutations were present in 1 of 48 ofloxacin-resistant isolates and 0 of 19 ofloxacin-susceptible isolates. CONCLUSIONS: In Singapore, genotypic analysis of resistance to PZA and ofloxacin is inadequate and should be complemented by conventional methods.     

pncA gene mutations in clinical isolates of tubercle bacillus by polymerase chain reaction-direct sequencing method: in relationship to pyrazinamide resistance]

We screened clinical isolates of tubercle bacillus for mutations in the pncA gene, which encodes pyrazinamidase (PZase), by polymerase chain reaction (PCR)-direct sequencing method. Sixty-eight strains of tubercle bacillus were isolated from 32 patients with pulmonary tuberculosis. The patients were treated with antituberculous agents including pyrazinamide (PZA) for 2 months. Thirty-two of the 68 strains were isolated from sputum samples collected from the patients before treatment; 29 strains and 7 strains were collected after 1 month and 2 months of treatment, respectively. The pncA genes in these strains, were assessed for mutations by direct sequencing of PCR products using an automated sequencer. Similarly, we examined two clinical isolates (ka567 and minami22) of tubercle bacillus, determined to be deficient in PZase activity by the Wayne method. A PZA-sensitive strain (H37Rv, ATCC27294), and a PZA-resistant strain (H37Rv-PZA-R, ATCC35828) were used as negative and positive controls for mutations in the pncA gene, respectively. None of the 68 strains demonstrated any mutations in the pncA gene; however, the 2 PZase-deficient strains had missense mutations in the pncA gene resulting in an amino acid substitution from His82 to Arg in clone ka567, and from Ala171 to Val in clone minami22.     

吡嗪酰胺耐药性结核分枝杆菌的噬菌体检测技术研究

目的 建立噬菌体生物扩增法（PhaB）快速测定吡嗪酰胺耐药性，并探讨其在结核分枝杆菌吡嗪酰胺耐药性测定中的应用价值。方法 应用建立的PhaB测定108株结核分枝杆菌临床分离株的吡嗪酰胺耐药性，并与绝对浓度法的药敏结果进行比较，对不符合的菌株进行最低抑菌浓度（MIC）测定和序列测定分析。结果 PhaB检测吡嗪酰胺耐药性的最佳测定条件为pH值5．5、药物浓度200μg／ml、37℃作用48h。用绝对浓度法检测108株结核分枝杆菌临床分离株，其中吡嗪酰胺敏感33株、耐药75株；用PhaB检测该108株结核分枝杆菌临床分离株，若以噬菌斑减少95％为判断标准。则吡嗪酰胺敏感32株，耐药76株。2种方法检测均为敏感的为28株，均为耐药的为71株，符合率为91．7％；2种方法检测结果不符的为9株，其中5株的PhaB结果与MIC结果相符，4株的结果不符，测序结果表明9株中有7株的PhaB结果与测序结果相符。如以绝对浓度法药敏结果为判断标准，PhaB检测吡嗪酰胺耐药性的敏感性为94．7％，特异性为84．8％，阳性预测值为93．4％，阴性预测值为87．5％，准确性为91．7％。结论 PhaB测定吡嗪酰胺耐药性简便、快速，3d即可获得药敏结果，可作为吡嗪酰胺耐药性的快速筛选方法。     

The curious characteristics of pyrazinamide: a review.

Pyrazinamide (PZA) is an important sterilising tuberculosis drug that helps to shorten the duration of current chemotherapy regimens for tuberculosis. When first discovered, it had activity in murine tuberculosis but no apparent in vitro activity, and its subsequent use in treatment depended largely on classic experiments at Cornell University, which showed its requirement for an acid pH for activity and its sterilising activity in the mouse. Recent studies have shown that PZA enters Mycobacterium tuberculosis by passive diffusion, is converted to pyrazinoic acid (POA) by nicotinamidase/pyrazinamidase (PZase) and is then excreted by a weak efflux pump. Protonated POA (HPOA) is reabsorbed into the bacilli under acid conditions and accumulates because the efflux pump is inefficient, causing cellular damage. Unlike other antibacterials, PZA has no defined target of action. PZA is more active against old than against actively growing cultures, probably because the energy production and efflux pump would be slowed down by low bacterial metabolism. This review deals with the activity of PZA in vitro, in macrophages and in animal models. It describes the evidence from clinical trials that it is an effective sterilising drug that acts synergistically with rifampicin. The highly diverse mutations in the PZase gene (pncA) that lead to loss of PZase activity cause PZA resistance. Methods for susceptibility determination either as tests against PZA or nicotinamide in liquid and solid media, as tests for PZase activity or for mutations in pncA, are reviewed.     

结核分支杆菌五种耐药基因检测的临床应用及评价

目的　检测结核分支杆菌rpoBkatG、rpsL、pncA和embB耐药基因 ,评价其临床应用价值。方法　采用聚合酶链反应 单链构象多态性 (PCR SSCP)分析和药敏试验 (比例法 ) ,了解 10 9例肺结核患者结核分支杆菌耐药情况 ,并分析、比较临床治疗效果。结果　 1/ 2以上的肺结核患者至少耐两种抗结核药物 ,对RFP、INH、SM、PZA和EB总耐药率分别为 80 7%、71 5 %、78 8%、5 7 7%和48 6%。rpoB、katG、rpsL、pncA和embB基因突变率分别为 76%、68%、71%、5 1%和 3 0 %。结核分支杆菌耐药基因突变率与耐药水平联系密切 ,多数结核分支杆菌耐药基因突变易发生在高耐药株 ,也有少数基因突变发生在低耐药株。根据药敏试验和耐药基因检测结果 ,6个月耐多药结核治愈率分别达到 5 4 8%和 62 8% ,治疗效果满意 ,两种方法差异无显著性 (P >0 0 5 )。结论　耐药基因检测指导治疗是一种新探索 ,PCR SSCP方法敏感、特异 ,可以快速检测结核分支杆菌rpoB、katG、rpsL、pncA和embB耐药基因突变 ,可能会成为临床指导用药的好方法     

Ethambutol resistance testing by mutation detection.

OBJECTIVE: To identify chromosomal mutations that confer resistance to ethambutol (EMB) in Mycobacterium tuberculosis. DESIGN: Drug-resistant (n = 235) and drug-susceptible (n = 117) M. tuberculosis isolates collected from the Western Cape in South Africa were subjected to embB gene analysis and the results were compared to phenotypic EMB testing. RESULTS: Genotypic analysis identified mutations at codon 306 of the embB gene in 20% (47/235) of the resistant isolates in comparison to only 1.7% (4/235) of those that were phenotypically resistant to EMB by the agar diffusion method. No gene mutations were detected in susceptible isolates. Phenotypic retesting in BACTEC demonstrated that the 47 genotypically resistant isolates were phenotypically resistant to EMB. This implies that 91.4% (43/47) of EMB resistance had been phenotypically missed by routine laboratory procedures. EMB resistance was closely linked to multidrug resistance (MDR); 87.2% (41/47) of the EMB-resistant isolates were resistant to both isoniazid and rifampicin. A newly developed one-step amplification refractory mutation system polymerase chain reaction (ARMS-PCR) method correctly detected the EMB-resistant genotype. CONCLUSION: Implementation of more accurate diagnosis of EMB resistance may enhance patient management in South Africa, as standardised treatment of MDR-TB with second-line drugs is currently dependent on the outcome of the EMB resistance test.     

Discrepant results between pyrazinamide susceptibility testing by the reference BACTEC 460TB method and pncA DNA sequencing in patients infected with multidrug-resistant W-Beijing Mycobacterium tuberculosis strains

BACKGROUND: Mycobacterium tuberculosis strains belonging to the W-Beijing family have received broad clinical and public health attention because of their rapid worldwide spread and their frequent association with outbreaks, multidrug resistance, and treatment failures and relapses. METHODS: The present study examined a large number of multidrug-resistant strain-W isolates (isolates of 29 patients) by susceptibility testing for pyrazinamide (PZA) using the reference BACTEC 460TB method (Becton Dickinson Diagnostic Instrument Systems; Sparks, MD) and also by DNA sequencing of the pncA gene. RESULTS: We found that despite of the presence of a strain W-specific Thr47Ala in the pncA gene, all strains showed susceptibility to PZA in the reference BACTEC 460TB system due to their higher minimum inhibitory concentrations (relative to BACTEC 460TB PZA-susceptible strains). CONCLUSIONS: Our results suggest that the current radiometric reference method cannot reproducibly detect PZA resistance in patients infected with W-Beijing strains. Therefore, PZA susceptibility testing should instead be based on analysis of the pncA gene for resistance-associated mutations.     

结核分支杆菌耐吡嗪酰胺分离株pncA基因突变的研究

目的 了解我国结核分支杆菌耐吡嗪酰胺（ＰＺＡ）分离株ｐｎｃＡ基因突变情况,研究其与耐ＰＺＡ之间的关系。方法 通过聚合酶链反应（ＰＣＲ）－单链构象多态性（ＳＳＣＰ）和ＰＣＲ－循环测序法（ＡＳ）分析７４株结核分支杆菌临床分离株的ｐｎｃＡ基因。以结核分支杆菌Ｈ３７ＲＶ标准株为对照。结果３２株药物敏感株ｐｎｃＡ基因ＳＳＣＰ分析未发现异常。２０株耐非ＰＺＡ药物的分离株中,１６株ｐｎｃＡ基因ＳＳＣＰ泳动正常;     

Study of the in vitro susceptibility of M. tuberculosis to ofloxacin in Spain. Spanish Study Group of M. tuberculosis resistance.

The aim of this study was to determine the proportion of antituberculosis ofloxacin resistance among Mycobacterium tuberculosis strain isolates in Spain. Over a period of one month, 213 M. tuberculosis strains collected from 14 different hospitals were studied, including strains both susceptible and resistant to primary antituberculosis drugs. In 28.1% of the strains, a minimum inhibitory concentration (MIC) for ofloxacin of 0.25 microg/ml was obtained; in 43.6% the MIC was 0.5 microg/ml; in 22.06% it was 1 microg/ml; and in 6.1% it was > or =2 microg/ml. Ofloxacin currently seems to be an effective antimicrobial in vitro against susceptible or multiresistant strains of M. tuberculosis in human immunodeficiency virus (HIV)-negative or HIV-positive patients in Spain.     

Absence of the genetic marker IS6110 from a strain of Mycobacterium tuberculosis isolated in Ontario

A 35-year-old female patient from Waterloo, Ontario was diagnosed with pulmonary tuberculosis in June 1995. Records indicated that the patient had emigrated from Laos circa 1990. A culture grown from a bronchoalveolar lavage specimen was identified as Mycobacterium tuberculosis by standard biochemical methods. Drug-susceptibility testing indicated the strain was resistant to pyrazinamide (PZA), and a mutation was detected within pncA, a gene associated with PZA resistance. Sequence data from the 16S rRNA gene and the 16S/23S rRNA gene spacer confirmed that the strain was a member of the M tuberculosis complex, and analysis of the mpcA and pncA genes supported the identification of the strain as M tuberculosis rather than Mycobacterium bovis. However, the insertion element IS6110, which is used for epidemiological tracing of M tuberculosis, was not detected in this strain by either restriction fragment length polymorphism analysis or by polymerase chain reaction. Two other genetic markers associated with the M tuberculosis complex, IS1081 and the direct repeat element, were present. The arrival of immigrants with tuberculosis from southeast Asia, where most strains of M tuberculosis lacking IS6110 have been traced, has important implications for epidemiological studies of tuberculosis in North America.     

Prevalence of katG Ser315 substitution and rpoB mutations in isoniazid-resistant Mycobacterium tuberculosis isolates from Brazil.

SETTING: Four hundred and sixty-eight isoniazid (INH) resistant Mycobacterium tuberculosis isolates recovered from a selected Brazilian population. OBJECTIVE: To check for susceptibility to other chemotherapeutic drugs used in TB treatment, and to ascertain mutations involved in INH and rifampicin (RMP) resistance. DESIGN: Antimicrobial susceptibility to RMP, streptomycin and ethambutol (EMB) was evaluated by the resistance ratio method and pyrazinamide (PZA) by activity assay. Single strand conformation polymorphism (SSCP) and sequence analysis were performed in samples from this panel to confirm mutations in codon 315 of the katG and in a 69-bp region of the rpoB gene. RESULTS: Combined resistance to INH+RMP, INH+ PZA, INH+EMB, and INH+RMP+PZA was shown in respectively 272 (58.1%), 126 (26.9%), 47 (10%), 116 (24.8%) isolates. No katG mutation was found in 19 (39.6%) of 48 strains tested. Ser315Thr substitution was found in 29 (60.4%). All RMP-resistant strains tested (n = 25) showed rpoB mutations. S531L substitution was found in 15 (60%). CONCLUSION: INH-resistant strains isolated from selected Brazilian populations frequently show resistance to other first-line anti-tuberculosis drugs. rpoB mutation was responsible for RMP resistance in all strains. Among INHr strains, katG mutations were shown in only 60.4%. Genetic approaches targeting the rpoB gene but not the katG gene have a high sensitivity to detect resistance among Brazilian M. tuberculosis strains.     

Pyrazinoic acid efflux rate in Mycobacterium tuberculosis is a better proxy of pyrazinamide resistance

Pyrazinamide is one of the most important drugs in the treatment of latent Mycobacterium tuberculosis infection. The emergence of strains resistant to pyrazinamide represents an important public health problem, as both first- and second-line treatment regimens include pyrazinamide. The accepted mechanism of action states that after the conversion of pyrazinamide into pyrazinoic acid by the bacterial pyrazinamidase enzyme, the drug is expelled from the bacteria by an efflux pump. The pyrazinoic acid is protonated in the extracellular environment and then re-enters the mycobacterium, releasing the proton and causing a lethal disruption of the membrane. Although it has been shown that mutations causing significant loss of pyrazinamidase activity significantly contribute to pyrazinamide resistance, the mechanism of resistance is not completely understood. The pyrazinoic acid efflux rate may depend on multiple factors, including pyrazinamidase activity, intracellular pyrazinamidase concentration, and the efficiency of the efflux pump. Whilst the importance of the pyrazinoic acid efflux rate to the susceptibility to pyrazinamide is recognized, its quantitative effect remains unknown. Thirty-four M.?tuberculosis clinical isolates and a Mycobacterium smegmatis strain (naturally resistant to PZA) were selected based on their susceptibility to pyrazinamide, as measured by Bactec 460TB and the Wayne method. For each isolate, the initial velocity at which pyrazinoic acid is released from the bacteria and the initial velocity at which pyrazinamide enters the bacteria were estimated. The data indicated that pyrazinoic acid efflux rates for pyrazinamide-susceptible M.?tuberculosis strains fell within a specific range, and M.?tuberculosis strains with a pyrazinoic acid efflux rate below this range appeared to be resistant. This finding contrasts with the high pyrazinoic acid efflux rate for M.?smegmatis, which is innately resistant to pyrazinamide: its pyrazinoic acid efflux rate was found to be 900 fold higher than the average efflux rate for M.?tuberculosis strains. No significant variability was observed in the pyrazinamide flux rate. The pyrazinoic acid efflux rate explained 61% of the variability in Bactec pyrazinamide susceptibility, 24% of Wayne activity, and 51% of the Bactec 460TB growth index. In contrast, pyrazinamidase activity accounted for only 27% of the Bactec pyrazinamide susceptibility. This finding suggests that mechanisms other than pncA mutations (reduction of pyrazinamidase activity) are also implicated in pyrazinamide resistance, and that pyrazinoic acid efflux rate acts as a better proxy for pyrazinamide resistance than the presence of pncA mutations. This is relevant to the design of molecular diagnostics for pyrazinamide susceptibility, which currently rely on pncA gene mutation detection.     

分析老年矽肺结核病的耐药水平与临床治疗

目的分析老年矽肺结核病的耐药水平和7种耐药基因突变情况。方法 117例老年矽肺结核患者的临床分离株均做传统梯度药敏试验和聚合酶链反应-单链构象多态性(PCR-SSCP)分析。结果被测菌株传统药敏试验耐药率82.1%。7种耐药基因[链霉素(rpsL)、利福平(rpoB)、异烟肼(katG)、乙胺丁醇(embB)、吡嗪酰胺(pncA)、喹诺酮(gyrA)、卡那霉素(km)]突变率分别为78.1%、65.6%、52%、33.3%、37.5%、54.1%、28.1%。结论传统梯度药敏试验与7种耐药基因联合检测,证实耐药基因突变与耐药水平和治疗关系密切。     

结核分枝杆菌对利福喷汀与利福平交叉耐药的实验研究

目的 观察利福喷汀对结核分枝杆菌的杀菌效力及其与利福平的交叉耐药性，探讨利福喷汀对结核分枝杆菌的实验室耐药界限，为临床应用利福喷汀治疗结核病，包括治疗对利福平耐药的结核病提供依据。方法 用7H9液体培养基、苏通液体培养基、改良罗氏固体培养基测定利福喷汀和利福平对结核分枝杆菌标准株(H37Rv)及临床分离的利福平敏感株、利福平耐药株的最低抑菌浓度(MIC)。结果 在7H9液体培养基上对临床分离的19株利福平敏感株分别测定利福平和利福喷汀的MIC，有80％利福平敏感株利福平的MIC≥0．32μg／ml，而利福喷汀的MIC多分布在0．02～0．32μg／ml之间(占84％)；无论标准株H37Rv、利福平敏感株(19株)或是利福平耐药株(45株)，利福喷汀对结核分枝杆菌的MIC普遍比利福平低2～4倍；利福喷汀敏感株和耐药株的MIC差别较大，在MIC为5～10μg／ml处能最大限度地区分敏感菌和耐药菌。结论 利福喷汀与利福平存在着交叉耐药，但利福喷汀比利福平有更强的杀菌效力，部分结核分枝杆菌对利福平达到临床耐药时，仍未达到利福喷汀临床耐药，对利福平耐药的部分结核分枝杆菌对利福喷汀仍具有一定程度的敏感性，提示临床上对利福平耐药的结核病患者使用利福喷汀可能有一定效果；实验结果对利福喷汀临界耐药界限进行了初步筛查，为利福喷汀常规药敏试验的开展提供了基本试验数据。     

耐异烟肼结核分枝杆菌临床分离株耐药相关基因突变研究

目的阐明结核分枝杆菌耐异烟肼临床分离株katG、inhA、ahpC、kasA及oxyR基因突变特点。方法对144株结核分枝杆菌临床分离株(耐异烟肼菌株101株;异烟肼敏感株43株)的katG、inhA、kasA、ahpC及oxyR基因进行DNA片断扩增及DNA序列分析,与GeneBank中结核分枝杆菌标准序列进行比较。结果(1)耐异烟肼菌株中未发现katG完全缺失,81株耐药株(80.2%)katG存在点突变、缺失或插入,其中16个突变位点未见报道;39株(38.6%)耐药株第315位点突变,低耐药菌株(1μg/ml)第315位点突变率显著高于高耐药菌株(10μg/ml;χ2=9.31,P<0.05);58株(57.4%)耐药株第463位点突变。23株(53.3%)敏感株第463位点突变。(2)5株(4.9%)耐药株inhA发生突变。敏感株inhA无突变。(3)3株(2.9%)耐药株ahpC发生突变。敏感株ahpC无突变。(4)17株(16.8%)耐药株kasA发生突变。敏感株中3株菌株Gly312Ser突变。(5)在全部菌株中未发现oxyR基因突变。(6)综合本项研究中各基因的突变情况,共有91株耐异烟肼菌株发生与异烟肼耐药相关的突变。结论本项研究进一步证实了结核分枝杆菌耐异烟肼与katG、inhA、ahpC及kasA基因突变之间的关系,并且提示还有其他机制参与异烟肼耐药。     

结核分枝杆菌链霉素耐药临床分离株rpsL基因突变特征分析

目的了解我国结核分枝杆菌（Mycobacterium tuberculosis,MTB）rpsL基因突变特征及其与链霉素耐药的相关性,并评价其应用价值。方法对302株结核分枝杆菌临床分离株的rpsL基因采用聚合酶链反应-直接测序（PCR-DS）进行检测。结果 59株对INH、RFP、SM、EMB和PAS全部敏感,rpsL基因没有突变,61株对SM敏感的耐药株有6株突变,SM敏感菌株突变率为5.00%（6/120）。182株SM耐药MTB,rpsL基因突变率为70.33%,其中43位密码子赖氨酸转变为精氨酸（Lys43Arg）突变率为52.20%;88位密码子有4种突变类型,突变率为17.58%;86位密码子精氨酸转变为谷氨酰胺（Arg86Gln）突变率为0.55%。SM耐药株的rpsL基因突变率明显高于SM敏感株的基因突变率,两者之间的差异有统计学意义,χ2=125.05,P〈0.05。结论 rpsL基因突变与结核分枝杆菌链霉素耐药高度相关,其中Lys43Arg突变是主要突变类型,PCR-DS检测rpsL基因突变可以用于临床结核菌链霉素耐药的快速检测。     

pncA mutations in clinical Mycobacterium tuberculosis isolates from Korea

Background  

Pyrazinamide (PZA) is among the first-line drugs for the treatment of tuberculosis. In vitro, it kills semidormant mycobacteria only at low pH. The purpose of this study was to compare PZA resistance with pyrazinamidase (PZase) activity and the genotype to better understand the molecular basis of PZA resistance and to expand the profile of pncA mutations worldwide.     

Universal pattern of RpoB gene mutations among multidrug-resistant isolates of Mycobacterium tuberculosis complex from Africa.

SETTING: Multidrug-resistant tuberculosis (MDR-TB) presents an increasing burden in Southern Africa. Rapid diagnostic tests for drug resistance to rifampicin have been developed based on mutation analysis of the rpoB gene. However, geographic differences of underlying mutations have recently been suggested. OBJECTIVE: Drug-resistant strains of Mycobacterium tuberculosis complex from Africa were analysed for geographic differences in frequency and location of rpoB mutations. DESIGN: A random sample of rifampicin-resistant strains was collected from 87 patients with pulmonary MDR-TB treated in 12 hospitals from six different regions of South Africa. In addition, 18 isolates of M. tuberculosis complex from Namibia, Sierra Leone, and Uganda, including 13 isolates of M. africanum, were analyzed. Point mutations were detected by direct sequence analysis of the rpoB gene. RESULTS: Missense mutations were identified for 91 isolates (87%). Double mutations were present in eight (8%) MDR-TB isolates, two of which carried one mutation outside a previously described diagnostic region. We found no geographic differences regarding the frequency and pattern of single rpoB gene mutations. CONCLUSION: Our results confirm that molecular genetic analysis of rifampicin resistance based on a core region within the rpoB gene is universally applicable to strains of M. tuberculosis complex from different geographic regions.