Application of the Roche Amplicor,Mycobacterium tuberculosis (PCR) test to specimens other than respiratory secretions

The ability of the Roche Amplicor, Mycobacterium tuberculosis (MTB) test to detect M. tuberculosis in specimens other than respiratory secretions was evaluated. A total of 249 specimens from 219 patients were tested. Of these, 12 specimens grew isolates of the M. tuberculosis complex and four grew isolates of the M. avium complex. The Amplicor MTB test was positive for 10 of the 12 specimens which grew M. tuberculosis and for three specimens which were culture negative. Two of the latter specimens were from patients with a clinical diagnosis of tuberculosis and with multiple sputum specimens which grew M. tuberculosis. Four specimens grew M. avium complex isolates, and all yielded negative Amplicor MTB test results. The sensitivity, specificity, and positive and negative predictive values for the Amplicor MTB test were 85.7%, 99.5%, 92.3%, and 99.1%, respectively. Our data indicate that the Amplicor MTB test will permit the rapid detection of M. tuberculosis in specimens other than respiratory secretions.     

Comparison of the BDProbeTec ET system with the roche COBAS AMPLICOR System for detection of Mycobacterium tuberculosis complex in the respiratory and pleural fluid specimens

The new BDProbeTec ET System (BDET; BD Biosciences, Sparks, MD) was compared with the Roche COBAS AMPLICOR System (CAS) and culture for Mycobacterium tuberculosis (MTB). A total of 253 specimens (152 respiratory and 101 pleural fluid specimens) collected from 240 patients were tested in parallel with the 3 assays. After resolving the discrepancies, the sensitivity, specificity, and positive and negative predictive values of the BDET for detecting MTB was 76.9%, 93.7%, 71.4%, and 95.2% for the respiratory specimens and 88.9%, 92.4%, 53.3%, and 98.8% for the pleural fluid specimens, respectively. The corresponding values of the CAS were 69.2%, 100%, 100%, and 94% for the respiratory specimens and 33.3%, 100%, 100%, and 93.9% for the pleural fluid specimens, respectively. No significant differences in sensitivities were observed between the results of both assays for the respiratory specimens. However, statistically significant differences in sensitivities were found between the BDET and CAS for the pleural fluid specimens (P =.02). Although the BDET was less specific than the CAS (P =.007), the BDET has an excellent sensitivity for detecting MTB in the pleural fluid specimens. Considering the low sensitivity of other available tests, the BDET can be a useful diagnostic tool for excluding MTB, particularly in the pleural fluid specimens.     

Clinical profile, laboratory characteristics and outcome in miliary tuberculosis

We report a retrospective series of 100 non-HIV adult patientswith miliary tuberculosis (MTB) treated in a tertiary care centre.There were 51 males. Their mean age was 35 years. Predisposingconditions existed in 34. Twelve patients had larger-than-miliary(>2mm) shadows in their chest roentgenograms. Five presentedwith acute respiratory failure, and early treatment cured fourof them. Hyponatraemia occurred in 42/60 patients (70%) forwhom values were available. Twelve patients (12%) died of MTB.Temperature     

Evaluation of the BACTEC MGIT 960 in comparison with BACTEC 460 TB for detection and recovery of mycobacteria from clinical specimens

The BACTEC MGIT system (M960), a fully automated, non radiometric instrument, designed for rapid detection of acid fast bacilli (AFB) from clinical specimens, was compared with the radiometric BACTEC 460 system (B460) and L?wenstein-Jensen (L-J) solid medium. A total of 1,093 respiratory and extrapulmonary specimens were decontaminated by the NALC-NaOH standard method, and randomly inoculated into the media. A total of 122 mycobacteria were recovered, including 47 Mycobacterium tuberculosis complex (MTB) isolates and 75 nontuberculous mycobacteria (NTM) isolates. Overall recovery rates were 59% for M960 system (p < 0.0001), 58.2% for L-J. medium (p < 0.0001) and 82% for Bactec 460 system, whereas rates for MTB alone were 91.5, 76.6 (p = 0.007), and 95.7%, respectively. The combination of M960 or B460 systems with L-J medium showed the same recovery rates for MTB strains (97.9%), whereas NTM rates were 68% (p < 0.0001) and 93.3%, respectively. Mean time to detection of smear-positive MTB, smear-negative MTB, and NTM were 12.2, 13.4, and 23.3 days, respectively, with the M960, 11.7, 21.3, and 24.8 days with the B460 and 20.4, 28.7, and 28.4 days with L-J medium. The M960 system showed a contamination rate of 9.8%, while B460 and L-J medium showed contamination rates of 4.3 and 3.8% respectively. In conclusion, the M960 system appeared to be accurate and rapid for the recovery of MTB, but reduced recovery of NTM and a high number of contaminated cultures deserve further study in order to assess if this system can represent a valuable alternative to the radiometric system.     

Performance of Xpert MTB/RIF Ultra assay on respiratory and extra-respiratory samples in a high-resource setting with a low tuberculosis prevalence

The Xpert MTB/RIF assay is a molecular assay that has improved the detection of tuberculosis and rifampicin resistance. However, its sensitivity is limited in patients with paucibacillary disease. Xpert MTB/RIF Ultra has been developed to resolve this limitation. We compared the performance of Xpert Ultra with that of culture for detection of Mycobacterium tuberculosis and rifampicin resistance. We reviewed laboratory records for 848 respiratory and 419 extrarespiratory samples that were processed between April 2018 and October 2019. The sensitivity, specificity, negative predictive value, and positive predictive value of Xpert Ultra were 94.8%, 98%, 98.8%, and 91.3% for respiratory samples and 83.8%, 96.9%, 98.4% and 72.1% for nonrespiratory ones. We found 26 culture-negative/Ultra-positive samples. Most of them have low bacillary burden and more than half belonged to patients with history of tuberculosis. Xpert Ultra demonstrates excellent diagnostic accuracy for tuberculosis detection, including paucibacillary specimens. In patients with history of tuberculosis, PCR results should be interpreted carefully.     

Potential of two nucleic acid amplification assays for quantifying mycobacterial load in respiratory and non-respiratory specimens: a prospective study

Quantification of bacillary load plays a critical prognostic role in tuberculosis patients. This study evaluated the potential of the Cepheid GeneXpert (GX) MTB/RIF and the BD ProbeTec system as quantitative assays. The time to positivity (TTP) measured by the Mycobacterial Growth Index Tube system was compared to the cycle threshold (C_t) of GX MTB/RIF and the Metric Other than Acceleration (MOTA) scores generated by the ProbeTec system. Out of 714 samples examined, 44 culture confirmed cases were identified. The C_t values in 21 respiratory samples showed a high linear fit with the TTP in liquid culture (Spearman's correlation coefficient r = 0.9, P value < 0.0001), which was not the case in 23 non-respiratory samples. In both types of specimens, the MOTA scores did not correlate with the TTP in liquid culture. This indicates the suitability of GX as a quantitative measurement of mycobacterial load in respiratory but not non-respiratory specimens.     

A naturally occurring point mutation in the rocA gene of Streptococcus pyogenes confers the highly virulent phenotype

IntroductionMucoid (MTB313) and nonmucoid (MTB314) strains of group A streptococcus (GAS) emm (antiphagocytic M protein) type 1 were simultaneously isolated from a single patient suffering from streptococcal meningitis. In a CD46-expressing transgenic (CD46 Tg) mouse model of subcutaneous infection into both hind footpads with MTB313 or MTB314, MTB313 showed considerably higher virulence than MTB314.MethodsThe comparative genomic analysis based on the whole-genome sequencing revealed that MTB313 possessed an amber codon within rocA (sensory transduction protein kinase), but MTB314 did not carry this stop codon. Thereafter, MAT101 was generated from MTB313 by introducing pRocA, which contained the full-length rocA from MTB314, into the cloning plasmid pLZ12-Km2. MAT100 was also generated by introducing pLZ12-Km2 into MTB313.ResultsAlthough MTB313 and MAT100 showed large quantities of cell-associated hyaluronic acid (HA) in the culture pellets, MTB314 and MAT101 showed small quantities of HA production. Finally, higher mortalities were observed in the MTB313- or MAT100-infected CD46 Tg mice than the MTB314- or MAT101-infected CD46 Tg mice.ConclusionsThese data indicate the possibility that a spontaneous point mutation in the rocA gene led to the highly virulent phenotype of M1 GAS.     

聚合酶链反应-测序技术快速检测耐异烟肼结核分枝杆菌KatG基因突变的研究

目的应用PCR-DNA测序技术快速检测耐异烟肼结核分枝杆菌分离株KatG基因突变,评价其在检测结核分枝杆菌异烟肼耐药性方面的应用价值。方法47株耐异烟肼结核分枝杆菌临床分离株及30株结核分枝杆菌敏感分离株用PCR-DNA测序技术检测KatG基因突变。结果47株耐异烟肼结核分枝杆菌分离株中,有31株KatG基因检出有突变,突变检出率为66.0%(31/47);30株结核分枝杆菌敏感株检出1株KatG基因突变。结论PCR-DNA测序技术方法敏感、准确、特异,可快速检测结核分枝杆菌KatG耐药基因突变,有利于耐异烟肼结核分枝杆菌耐药性的快速检测。     

Processing of Mycobacterium tuberculosis antigen 85B involves intraphagosomal formation of peptide-major histocompatibility complex II complexes and is inhibited by live bacilli that decrease phagosome maturation.

Mycobacterium tuberculosis (MTB) inhibits phagosomal maturation to promote its survival inside macrophages. Control of MTB infection requires CD4 T cell responses and major histocompatibility complex (MHC) class II (MHC-II) processing of MTB antigens (Ags). To investigate phagosomal processing of MTB Ags, phagosomes containing heat-killed (HK) or live MTB were purified from interferon-gamma (IFN-gamma)-activated macrophages by differential centrifugation and Percoll density gradient subcellular fractionation. Flow organellometry and Western blot analysis showed that MTB phagosomes acquired lysosome-associated membrane protein-1 (LAMP-1), MHC-II, and H2-DM. T hybridoma cells were used to detect MTB Ag 85B(241-256)-I-A(b) complexes in isolated phagosomes and other subcellular fractions. These complexes appeared initially (within 20 min) in phagosomes and subsequently (>20 min) on the plasma membrane, but never within late endocytic compartments. Macrophages processed HK MTB more rapidly and efficiently than live MTB; phagosomes containing live MTB expressed fewer Ag 85B(241-256)-I-A(b) complexes than phagosomes containing HK MTB. This is the first study of bacterial Ag processing to directly show that peptide-MHC-II complexes are formed within phagosomes and not after export of bacterial Ags from phagosomes to endocytic Ag processing compartments. Live MTB can alter phagosome maturation and decrease MHC-II Ag processing, providing a mechanism for MTB to evade immune surveillance and enhance its survival within the host.     

结核菌素皮肤试验阳性人群是否应该接受化学预防治疗

结核病是我国常见的呼吸道传染病之一,发病率和死亡率仍居传染病之首。WHO估计全球有1/3的人口感染结核分枝杆菌(MTB),即潜伏结核感染者(LTBI),而我国是结核病高负担国家之一,大约有40%⁴5%的人口感染MTB。LTBI者在2年内发展成为有临床表现的活动性结核病的风险为5%45%的人口感染MTB。LTBI者在2年内发展成为有临床表现的活动性结核病的风险为5%¹0%,如果采取化学预防,可以降低LTBI者2年内的发病率。LTBI的检测最常用的方法是结核菌素皮肤试验(TST),但并非所用TST阳性人群均适宜化学预防。在我国对于TST强阳性人群,尤其是结核病的高危人群,适合采取化学预防治疗。预防方案可以是单药异烟肼,也可以是异烟肼联合利福平或利福喷汀预防治疗,疗程及给药方式没有统一标准。     

Xpert MTB/RIF检测痰标本结核分枝杆菌与利福平耐受性的临床应用研究

目的分析Xpert MTB/RIF方法用于临床快速检测结核分枝杆菌(MTB)与利福平耐受性的临床意义。方法收集2015年1-12月在惠州市结核病防治研究所及5个县区医院结核科就诊的肺结核患者痰标本552例,进行涂片镜检、Xpert MTB/RIF核酸检测和改良罗氏培养,并对培养阳性者进行药敏实验。评价各种方法 MTB检测灵敏度与特异度,对比传统药敏方法和Xpert MTB/RIF检测利福平耐药性的结果并分析。结果 Xpert MTB/RIF与改良罗氏培养法对MTB检测结果相比,敏感度95.3%、特异度93.1%;耐药性对比结果中,所有阳性标本中利福平耐药的敏感度82.1%,特异度97.8%;Xpert MTB/RIF检测MTB分级与改良罗氏培养分级一致性分析中,kappa=0.688,提示两者结果具有良好的一致性。结论 Xpert MTB/RIF可用于临床早期快速检测结核分枝杆菌与利福平耐药检测的筛查,有利于临床快速决策。     

环介导等温扩增技术快速检测结核分枝杆菌核酸

摘要:目的：建立一种快速准确的检测结核分枝杆菌（MTB）核酸的环介导等温扩增（LAMP）方法。 方法：以重复插入序列IS6110为目的基因,设计LAMP引物,特异检测MTB核酸。用本法与痰涂片抗酸染色镜检法、实时荧光PCR法对100例可疑患者痰标本进行对比检查。 结果：LAMP法特异性强,仅扩增MTB复合群核酸;灵敏度高,检测限达100 fg;而实时荧光PCR检测限为1 pg。对100例疑似结核病患者痰液标本检测,涂片抗酸染色法、LAMP法、实时荧光PCR法的阳性率分别为28%、39%和38%。 结论：本研究建立的LAMP方法检测MTB核酸特异性强、灵敏度高、时间短且操作简便,有望成为临床快速检测MTB的新方法。     

结核分枝杆菌L型的培养及临床研究

目的探讨肺结核患者结核分支杆菌L型培养结果与临床状况的关系。方法对151例活动性肺结核、31例非活动性肺结核、27例非肺结核作痰结核分支杆菌L型培养,并分别作痰抗酸涂片、培养、PCR检测,结核分支杆菌L型培养阳性病例进行病程长短、初复治、有无空洞的比较;对70例活动性肺结核、12例非活动性肺结核作外周血结核分支杆菌L型培养。结果151例活动性肺结核、31例非活动性肺结核、27例非肺结核痰结核分支杆菌L型培养阳性分别为30例、3例、0例,其中87例抗酸染色与罗氏培养均阴性的活动性肺结核结核分支杆菌L型培养阳性12例(13.79%)。病程大于12月者明显高于小于1月者(P<0.01),复治病人明显高于初治病人(P<0.01),有空洞者明显高于无空洞者(P<0.05)。结论结核病患者L型结核菌的存在是结核病难治、复发的主要原因之一。开展痰、血等标本的结核分支杆菌L型检测,对于提高结核病诊断正确率有重要意义。     

结核分枝杆菌mpt64基因突变研究

目的分析结核分枝杆菌(Mycobacterium tuberculosis,MTB)mpt64基因突变情况。方法提取MTB标准株H37Rv和45株MTB临床株的DNA,扩增mpt64基因并进行序列分析。结果 MTB标准株H37Rv和44株MTB临床株的mpt64基因无突变,1株MTB临床分离株的mpt64基因存在63个碱基的缺失突变。结论结核分枝杆菌mpt64基因突变频率低。     

Antimicrobial activity of clofazimine is not dependent on mycobacterial C-type phospholipases

We have used a phospholipase C (PLC)-deletion mutant (plcABC) of the H37Rv strain of Mycobacterium tuberculosis (MTB), as well as a plcA-insertion mutant of Mycobacterium smegmatis, to investigate the possible involvement of PLCs in clofazimine-mediated inhibition of mycobacterial K(+) transport and growth. Inactivation of the PLCs of MTB and insertion of the plcA gene into M. smegmatis resulted in a substantial reduction and increase in hydrolysis of phosphatidylcholine (PC), respectively. However, both the mutant and wild-type strains of MTB and M. smegmatis were equally sensitive to the inhibitory effects of clofazimine on K(+) uptake and growth. These observations demonstrate that the PLCs of MTB are not involved in the antimicrobial activity of clofazimine.     

Determination of ethambutol MICs for Mycobacterium tuberculosis and Mycobacterium avium isolates by resazurin microtitre assay

OBJECTIVES: To test susceptibilities of Mycobacterium tuberculosis (MTB) isolates to ethambutol by the L?wenstein-Jensen (LJ) proportion method and resazurin microtitre assay (REMA) and to evaluate REMA for the determination of ethambutol MICs for MTB and Mycobacterium avium isolates. METHODS: A total of 50 MTB and 20 M. avium isolates were tested to determine the MICs of ethambutol by REMA and agar dilution method. MTB isolates were also tested by the LJ proportion method. RESULTS: REMA provided ethambutol susceptibility results for all the isolates within 8-9 days. For MTB isolates, REMA showed 96.7% sensitivity, 100.0% specificity and 98.0% accuracy when LJ proportion results were taken as 'gold standard'. For both MTB and M. avium isolates, the MICs determined by REMA were lower than those determined in agar medium, indicating that MIC values determined by REMA are closer to the actual MICs for the isolates. CONCLUSIONS: REMA can be used as a rapid and inexpensive method for mycobacterial drug susceptibility testing against ethambutol. In comparison with the agar method, the MICs determined by REMA can more accurately be correlated with achievable plasma concentrations of antimycobacterial agents.     

Genetic and phenotypic characterization of drug-resistant Mycobacterium tuberculosis isolates in Hong Kong

OBJECTIVES: To characterize 250 drug-resistant Mycobacterium tuberculosis (MTB) isolates in Hong Kong with respect to their drug susceptibility phenotypes to five common anti-tuberculosis drugs (ofloxacin, rifampicin, ethambutol, isoniazid and pyrazinamide) and the relationship between such phenotypes and the patterns of genetic mutations in the corresponding resistance genes (gyrA, rpoB, embB, katG, inhA, ahpC and pncA). METHODS: The MIC values of the aforementioned anti-tuberculosis drugs were determined for each of the 250 drug-resistant MTB clinical isolates by the absolute concentration method. Genetic mutations in the corresponding resistance genes in these MTB isolates were identified by PCR-single-stranded conformation polymorphism/multiplex PCR amplimer conformation analysis (SSCP/MPAC), followed by DNA sequencing of the purified PCR products. RESULTS: Resistance to four or five drugs was commonly observed in these MTB isolates; such phenotypes accounted for over 34% of the 250 isolates. The most frequently observed phenotypes were those involving both rifampicin and isoniazid, with or without additional resistance to the other drugs. A total of 102 novel mutations, which accounted for 80% of all mutation types detected in the 7 resistance genes, were recovered. Correlation between phenotypic and mutational data showed that genetic changes in the gyrA, rpoB and katG genes were more consistently associated with a significant resistance phenotype. Despite this, however, a considerable proportion of resistant MTB isolates were found to harbour no detectable mutations in the corresponding gene loci. CONCLUSIONS: These findings expand the spectrum of potential resistance-related mutations in MTB clinical isolates and help consolidate the framework for the development of molecular methods for delineating the drug susceptibility profiles of MTB isolates in clinical laboratories.     

基因检测及MODS技术快速诊断结核分枝杆菌对左氧氟沙星的敏感性研究

目的 探讨基因检测技术和显微镜观察药物敏感度检测技术(MODS)对结核分枝杆菌(MTB)耐左氧氟沙星(LFX)快速诊断价值.方法 选取MTB标准株(H37Rv)和32株耐LFX临床分离株,行gyrA基因喹诺酮类药物耐药决定区(QRDR)序列测定,同时,用24孔细胞培养板进行MTB液体药敏检测.结果 基因检测结果显示,H37Rv未发生gyrA基因突变;与H37Rv株序列的差异比较显示,29株耐LFX临床株发生了有义突变,突变率90.6%.MODS与罗氏绝对浓度法药敏(L-J)比较,H37Rv完全相符;32株耐LFX临床分离株,相符31株,不符1株,符合率为96.9%.结论 gyrA基因突变检测可作为快速诊断结核分枝杆菌对LFX敏感性的一种方法,但不能完全区别低耐药和高耐药而使用受到限制.MODS技术检测LFX耐药性具有快速、操作简便、灵敏度和特异性高等优点,可作为结核分枝杆菌对LFX敏感性的快速检测新方法.     

实时荧光定量PCR检测血浆结核分枝杆菌DNA的初步临床应用

目的 评价实时荧光定量PCR技术检测血浆（或血清）结核分枝杆菌（Mycobacterium tuberculosis,MTB）DNA的技术。方法 建立实时荧光定期量PCR方法测定血浆MTB DNA,分别检测临床确诊的55例结核病患者血清43份,血浆25份以及非结核肺部疾病患者血清18份,健康体检血清18份和健康体检者血浆11份的MTB DNA含量。结果 18例非结板肺疾病患者血清、18例健康体检者血清以及11例健康体检者血浆MTB DNA全部阴性。55例初诊结核患者中10例（18．2％）治疗前血浆（或血清）MTB DNA阳性。在痰涂片阴性的18例结核患者中,血浆（或血清）MTB DNA阳性检出率为27．8％（5／18）,其特异性达100％。结论 本研究证实了结核患者血浆（或血清）循环MTB DNA的存在,其定量检测对痰涂片阴性及无痰患者的结核病诊断有重要参考价值。     

结核分枝杆菌临床分离株对三种氟喹诺酮类药物的敏感性分析研究

目的对结核分枝杆菌（MTB）临床分离株对氧氟沙星（OFX）、左氧氟沙星（LFX）和莫西沙星（MFX）三种临床常用的氟喹诺酮类药物的敏感性进行分析研究,为临床用药提供依据。方法本研究采用液体培养基联合MTT技术进行抗结核药物的最低抑菌浓度（MIC）检测。对来自我院不同结核病患者的163株MTB临床分离株进行0FX、LFX、MFX三种药物的MIC检测和BactecMGIT960药敏检测。结果163株中OFX耐药株占35．6％;耐多药（MDR）结核菌株中,OFX耐药率为73．5％,MDR菌株中LFX耐药率超过一半以上;所有MTB菌株MFX的MIC值均≤1μg／ml。结论目前在MTB临床分离株中,OFX和LFX已出现较高的耐药率,值得引起临床医生的重视,MFX在MDR结核和广泛耐药（XDR）结核中显示出良好的抗菌效果,给MDR结核病的治疗带来希望。