Specificity of insertion sequence-based PCR assays for mycobacterium tuberculosis complex.

OBJECTIVE: To determine the specificity of different insertion sequence-targeted polymerase chain reaction (PCR) tests for Mycobacterium tuberculosis complex. DESIGN: One M. bovis BCG strain, two M. tuberculosis strains and ten species of mycobacteria other than tuberculosis (MOTT) were tested by three PCR assays based on the repetitive elements IS6110, IS1081 and IS990 under variable amplification conditions (different temperatures of primer annealing and numbers of reaction cycles). RESULTS: DNA amplifications based on the three insertion sequences yielded fragments of expected sizes only in DNA from M. tuberculosis complex strains when the tests were conducted at high stringency (65 degrees C). At the annealing temperature of 60 degrees C the PCR assay with IS6110-specific primers yielded a 245 bp fragment also in nine MOTT strains tested. This could result from previously reported homology between non-tuberculous mycobacteria and a central region of IS6110. Amplification assays based on IS1081 and IS990 gave false-positive results in some MOTT isolates only under very low stringency (55 degrees C), which could be due to non-specific priming of the target DNA at that temperature. CONCLUSION: Repetitive elements IS1081 and IS990 may represent a more reliable alternative to the more widely used IS6110 PCR target for tuberculosis diagnosis.     

Development and evaluation of a multiplex polymerase chain reaction for the detection of Mycobacterium tuberculosis from pulmonary specimens

Abstract Background: The diagnosis of pulmonary tuberculosis is still a major challenge. Using a polymerase chain reaction (PCR), one can detect Mycobacterium tuberculosis in clinical samples within a few hours. However, single gene targets may result in false negativity due to the absence of target DNA in some M. tuberculosis isolates. The objective of this study was to develop and evaluate a multiplex PCR (M-PCR) using IS6110 and devR primers for the detection of M. tuberculosis in sputum samples. Methods: Sputum samples were collected from: (1) 200 confirmed cases of tuberculosis; (2) 100 suspected cases of tuberculosis diagnosed on the basis of clinical and radiological findings; (3) 200 non-tubercular patients suffering from respiratory diseases other than tuberculosis, in whom tuberculosis had been excluded. All 500 sputum samples were subjected to PCR using IS6110 primers, and M-PCR using IS6110 and devR primers; results were compared with conventional techniques. Results: It was found that M-PCR was 97.5% successful in detecting the presence of tuberculosis in the confirmed tuberculosis group as compared to 84.5% by IS6110-based PCR. In the suspected tuberculosis group, M-PCR could detect 45% of cases as compared to 40% by IS6110-based PCR. Overall, the specificities of both the PCR and M-PCR were found to be 96.5%. Conclusions: This study demonstrated that the M-PCR assay is more sensitive than the IS6110-based PCR for the detection of M. tuberculosis in sputum specimens and could be applied in situations of highly suspected tuberculosis when all others tests including IS6110 PCR are negative.     

Detection of Mycobacterium tuberculosis in sputum samples using a polymerase chain reaction

A polymerase chain reaction (PCR) assay for the rapid detection of Mycobacterium tuberculosis in sputum samples is described. The target DNA is a 123-base pair (bp) segment of IS6110, which is repeated in the M. tuberculosis chromosome and is specific for the M. tuberculosis complex. Methodology used to lyse the mycobacteria, extract the DNA, and amplify the 123-bp target DNA is presented. The amplified PCR product is detected by examination of ethidium-bromide-stained acrylamide gels. An internal control using the same primers as the target DNA has been constructed to assess the efficacy of each individual reaction. Of 162 sputum samples tested, 82 were smear-positive for acid-fast bacilli. Of the 94 specimens from patients in whom pulmonary tuberculosis was diagnosed, 51 were culture-positive, smear-positive, or both. Fifty of these were PCR positive. Of the 42 specimens from patients with nontuberculous mycobacterial pulmonary disease, 41 were PCR negative. All 26 specimens from patients without mycobacterial infection were PCR negative. This assay provides a sensitive and specific means for the laboratory diagnosis of tuberculosis within 48 h that is relatively simple to perform.     

Simultaneous use of two PCR systems targeting IS6110 and MPB64 for confirmation of diagnosis of tuberculous lymphadenitis

PCR has emerged as a powerful technique for detection of various pathogens including Mycobacterium tuberculosis. In present study, eighty one samples of lymph node biopsies from clinically suspected cases of tuberculous lymphadenitis were examined for AFB, culture on L?wenstein Jensen medium and simultaneous use of two PCRs targeting IS6110 and MPB64. Positivity with M. tuberculosis culture and AFB was 13.6% and 28.4% respectively. All samples culture positive for nontuberculous mycobacteria were negative by both PCR systems. Higher proportion of positive results were observed with PCR targeting IS6110 by which 56 of 81 (69.1%) samples showed positive results as compared to PCR targeting MPB64 by which 39 of 81 (48.2 %) samples showed positive results. When combined, 63 out of 81 (77.8%) samples were detected positive for M. tuberculosis DNA. However, 7/81 (8.6 %) samples remained negative by IS6110 but positive by MPB64 method. Thus our data suggest that the use of one additional PCR (other than IS6110 system) can reduce false negativity of PCR results in the samples harboring zero copy of IS6110 element which is known to exist in Indian population.     

Method for efficient storage and transportation of sputum specimens for molecular testing of tuberculosis.

SETTING: The polymerase chain reaction (PCR) is a highly sensitive method for the detection of Mycobacterium tuberculosis and is available in most countries, though to a lesser extent in rural areas. OBJECTIVE: To amplify M. tuberculosis DNA sequences of sputum spotted on FTA cards and compare them with the results of microscopic examination among culture-positive samples. DESIGN: A total of 102 sputum specimens of TB patients in treatment were spotted on FTA cards and stored at room temperature until DNA analysis. We assessed the IS6110 region of M. tuberculosis. The efficacy of the PCR assay for the direct detection of M. tuberculosis was evaluated and compared with the results of cultures (Middlebrook 7H9 broth) and smears of fresh sputum specimens. RESULTS: We were able to detect 10 fg/microl of mycobacterial DNA even after 6 months in storage. The PCR sensitivity and specificity using the FTA card system were 82% and 96%, while microscopic examination showed 41% and 95%, respectively. CONCLUSION: The FTA card system for the storage of bacterial DNA from sputum samples should be considered for the molecular diagnosis of tuberculosis. Samples can easily be obtained from geographically isolated populations and shipped by mail for accurate molecular diagnosis.     

Detection of Mycobacterium tuberculosis in clinical samples using insertion sequences IS6110 and IS990

To detect Mycobacterium tuberculosis in clinical samples, we used the M. tuberculosis-complex specific insertion sequence IS990 as the target in a simple DIG-PCR ELISA assay, as this element is present as a single copy in all strains of M. tuberculosis we have examined to date. The IS990 test was compared with a similar PCR that utilizes IS6110 as target. For detection of PCR product, digoxigenin-11-dUTP (DIG-dUTP) was incorporated into the product. After amplification, the PCR product was hybridized with biotinylated capture probe, which was complementary to the inner part of the amplicon. The hybrid was captured onto streptavidin-coated microtiter plate and DIG-labeled PCR product was detected using a peroxidase-conjugated antibody to DIG. We evaluated DIG-PCR ELISA for the detection of M. tuberculosis DNA in 265 respiratory and non-respiratory specimens taken from patients with known and suspected tuberculosis disease or from controls. The sensitivity and specificity of both IS990-based test and IS6110-based test was 96.5% and 95.3% respectively, comparable to the sensitivity and specificity of the IS6110-based test. The results demonstrate that the IS990 PCR ELISA test is a rapid and sensitive tool for the detection and identification of M. tuberculosis in clinical samples, and may have advantages to the more widely used IS6110-based tests, particularly in areas where IS6110-negative strains are found.     

Detection of Mycobacterium tuberculosis by a polymerase chain reaction colorimetric dot-blot assay.

SETTING: A public health laboratory in a tuberculosis-endemic region in Brazil. OBJECTIVE: To evaluate the accuracy of a combined polymerase chain reaction (PCR) colorimetric dot-blot protocol for Mycobacterium tuberculosis detection in clinical samples in a public health laboratory. DESIGN: Eighty clinical samples (13 cerebrospinal fluid, 31 induced sputum, 17 expectorated sputum, eight bronchoalveolar lavage and 11 pleural fluid) were assayed with the developed protocol. The accuracy of polymerase chain reaction (PCR) dot-blot methodology was compared to PCR agarose gel electrophoresis (PCR-AG) using as a gold standard the bacteriological result (culture and biochemical identification) combined with clinical follow-up. One internal region of the IS6110 repetitive element of the M. tuberculosis complex was selected for amplification and the amplified product transferred to nylon membranes to be detected by biotinylated DNA probe. RESULTS: Overall sensitivity and specificity obtained were respectively 90% and 97% for PCR-AG and 95% and 97% for the PCR dot-blot. Among the 56 respiratory specimens, the sensitivity and specificity results for PCR-AG were respectively 88% and 95%, and for PCR dot-blot they were 94% and 95%. Among the 24 non-respiratory specimens the sensitivity and specificity results were respectively 83% and 100% for PCR-AG, and 100% and 100% for the PCR dot-blot protocol. CONCLUSION: The results demonstrated that the PCR dot-blot assay may be helpful in the diagnosis of tuberculosis, and feasible even in resource-poor countries.     

AmpliSensor—聚合酶链反应定量检测肺结核患者外周血结 …

目的 探讨ＡｍｐｌｉＳｅｎｓｏｒ－聚合酶链反应定量检测外周血中结核分支杆菌ＤＮＡ在肺结核的应用价值。方法 采用ＱｌＡａｍｐ和ＡｃｕＰｕｒｅ法提取，制备全血中模板ＴＢ－ＤＮＡ，应用ＡｍｐｌｉＳｅｎｓｏｒ－ＰＣＲ定量检测，并与ＩＳ６１１０－单管巢式聚合酶链反应（ＳＮ－ＰＣＲ）作比较。结果２００例肺结核患者的血液标本中，两种方法测得结核分支杆菌ＤＮＡ的阳性率分别为６０．５％、６３．５％。８５例非结核肺病     

Simple microplate hybridization assay for detection of amplified products of Mycobacterium tuberculosis

We describe a simple microplate hybridization assay for the rapid detection of the IS6110 PCR products of Mycobacterium tuberculosis from clinical cultures and from sputum specimens. The assay is based on the specific detection with a fluorescein-labeled detection probe of biotinylated PCR products which are captured on avidin coated microplate. Hybridized products with fluorescein were identified by using anti-fluorescein antibody, horseradish peroxidase conjugate and colorimetric peroxidase substrate. The specificity of the assay was assessed by analysis of 56 bacterial strains: the assay discriminated perfectly between the positive and negative groups when an OD490 of 0.18 was used as the cut-off point. The assay was sensitive enough to detect as little as 1 pg of M. tuberculosis H37Rv DNA, which is equivalent to approximately three bacilli. To evaluate the assay performance clinically, 190 sputum samples from newly diagnosed TB patients were tested; 79 were classified as TB positive, and 111 were classified as TB negative by culture and acid-fast staining as the 'gold standard'. The sensitivity, specificity and accuracy of the PCR-microplate hybridization assay were 90, 100 and 96%, respectively. The total assay time of hybridization following the PCR was 4 hours. The PCR-microplate hybridization assay is fast, simple and accurate and is suitable for use in the microbiology laboratory or for the analysis of large numbers of samples.     

一种直接检测结核病痰标本的PCR技术的建立与评价

目的建立并评价聚合酶链式反应(polymerase chain reaction,PCR)在结核病痰标本检测中的应用价值。方法根据结核分枝杆菌复合体IS6110序列设计引物INS1和INS2,并建立PCR反应体系和反应条件。运用PCR方法分别检测标准菌株、结核分枝杆菌PCR检测标准品和拟诊结核病患者痰标本,采用痰涂片和细菌培养为对照。结果比较的统计学分析采用卡方检验。结果PCR方法对结核分枝杆菌、牛分枝杆菌、卡介苗标准株的最小检出浓度分别达到102,103,103个细菌/毫升,能够特异地检出结核分枝杆菌复合体。在PCR检测的574例拟诊病例中,PCR检测阳性病例241例,42%;痰涂片和细菌培养的阳性率分别为19.69%和26.31%,PCR检测阳性率高于传统细菌学检验方法,经χ2检验,差异具有显著统计学意义(χ2=103.67,P<0.01)。以痰培养结果为标准,计算PCR检测方法的敏感度为67.53%。结论PCR检测方法与传统的细菌学检测方法相比可以提高阳性标本检出率,而且具有快速、特异、简便的特点,有望成为结核病大规模筛查和临床快速检测方法。     

Molecular characterization of Mycobacterium tuberculosis isolated in the State of Parana in southern Brazil

Sequence IS6110 has been successfully used throughout the world for characterizing the Mycobacterium tuberculosis lineages. The aim of this study was to obtain data about circulating strains of M. tuberculosis in patients from the State of Parana in southern Brazil. Sixty-two clinical specimens obtained from sputum, bronchial aspirate, biopsy and urine from 62 patients clinically diagnosed with tuberculosis and admitted to the SUS-Brazil - The Brazilian Centralized Health Service System - were genotyped by the mixed-linker PCR DNA fingerprinting technique. The analysis demonstrated that the number of copies of the IS6110 sequence per isolates varied from four to 13 bands, with an average number of 8.5. From this, 93% of the isolates presented multiple copies. Isolates with no copies of the IS6110 element were not observed. The genetic analysis by UPGMA grouped the 62 isolates by similarity into three different groups: the first group contained two strains, the second was composed of 23, and the third, a more heterogeneous group, contained 37 isolates. Only two isolates (3.2%) formed a cluster; in other words, they presented a pattern of polymorphism with similarity above 95%. Such findings suggest that in the State of Parana, illness predominantly develops through reactivation of the latent infection as opposed to exogenous transmission. The methodology used (mixed-linker PCR DNA fingerprinting) allowed for 93.5% differentiation of the isolates tested, and proved to be a powerful tool for differentiation in the molecular genotyping of M. tuberculosis.     

Comparative evaluation of IS6110 PCR via conventional methods in rapid diagnosis of new and previously treated cases of extrapulmonary tuberculosis

In developing countries the diagnosis of extrapulmonary tuberculosis (EPTB) is a major burning challenge. EPTB encounters many problems like pauci-bacillary nature, inadequate specimen volume. All the limitations reflect in the poor contribution of conventional bacteriological technique in the establishment of diagnosis of EPTB. Nucleic acid amplification methods are rapid and sensitive has modified strategies for the detection of mycobacterial DNA. A fragment of DNA of 123 bp belonging to insertion sequence IS6110 based on specific gene of Mycobacterium tuberculosis complex was amplified by polymerase chain reaction (PCR) for the rapid diagnosis of EPTB. The present study was to comparative evaluation of IS6110 PCR via conventional methods in the rapid diagnosis of new and Previously treated cases of extra pulmonary tuberculosis. Four hundred fifty specimens were collected from suspected cases of EPTB were processed for Mycobacteria by Zeihl Neelson (ZN) staining and BACTEC culture for M. tuberculosis. All the specimens were also processed for IS6110 based PCR amplification with primers targeting 123 bp fragment of insertion element IS6110 of M. tuberculosis complex. We found significant difference was seen in sensitivities of different tests. Of these 450 specimens, 60 (13.4%) were positive for AFB by ZN staining, 202 (45%) for BACTEC culture and IS6110 PCR were positive for M. tuberculosis complex in 283 (63%) specimens (p< 0.05). However, there was no significant difference (p< 0.05) as far as specificity of different tests. We found that IS6110 PCR has higher sensitivity than smear microscopy and BACTEC culture in both cases of new cases as well as in previously treated cases. IS6110 PCR can be highly useful in diagnosis of new and treated cases of EPTB. It may facilitate therapeutic decisions for those with suspected of EPTB.     

结核分枝杆菌IS6110序列在石蜡组织中的检测、克隆与测序

目的：探讨套式-聚合酶链反应（Nested-PCR)检测石蜡组织中结核分枝杆菌的特异性和敏感性。方法：采用套式-PCR检测石蜡包埋组织中结核菌复合体特异插入序列IS6110，并对部分标本的PCR产物进行克隆和测序。结果：31例结核标本石蜡组织检出结核菌DNA共28例，套式-PCR的敏感度为90.3%,特异度为100%。阳性预测值为100%。随机选取两例PCR产物没是序结果与结核菌标准株H37Rv同源性分别为97%和95.3%。结论：套式-PCR检测常规石蜡包埋组织中结核菌IS6110序列具有特异性强和敏感性高的特点，可应用于临床诊断，尤其是对那些常规苏木精-伊红染色和抗酸染色无法确诊的病例更具意义。     

利用PCR技术检测537份新疆结核病人痰标本中的结核分枝杆菌

目的 提高聚合酶链反应在检测人结核分枝杆菌中的特异性和敏感性。方法 在聚合酶链反应中对4种DNA片段即结核杆菌特异插入列IS6110,IS1081,和16SrRNA,65kDa摸板进行了比较;为获取较多的细菌DNA,临床痰标本处理采用了国际标准化方法主要包括用一定量的N－乙酰－L半胱胺酸和氢氧化钠处理痰标本;改进了RCR混和液的成份即添加了甘油,dUTP－尿嘧啶糖基化酶。结果 选择IS6110作为结核杆菌特异性摸板用于检测细菌DNA,制备出了6批人结核杆菌PCR检测试剂盒,在对来自新疆结核病研究所的537份痰标本的检测中发现,谝试剂盒检测的特异性为65.97%,敏感性为93.53%。结论 改良TB－PCR试剂盒显示有较高的敏感性,特异性还有待于进一步完善,该试剂盒在临床诊断中有一定的价值。     

Evaluation of Amplicor- and IS6110-PCR for direct detection of Mycobacterium tuberculosis complex in Singapore

One hundred and seventy-eight samples from 168 individuals were tested for Mycobacterium tuberculosis complex ( Mtc ) using Amplicor PCR, IS6110 -PCR (in-house), acid fast (AF)-staining and culture. Thirty-one samples were positive by culture, but 37 samples were later resolved to be truly positive for Mtc . Of these, Amplicor detected 32 (86.5%), IS6110 -PCR detected 31 (83.6%), and AF-staining 21 (56.8%). None of the 141 Mtc -negative samples was positive by these tests, thus giving 100% specificity. Although the IS6110 -PCR was more sensitive than Amplicor in detecting spiked Mtc DNA, it was not more sensitive than the latter in detecting Mtc in clinical samples. Reasons likely to account for the PCR false negativity were (i) sample inoculum size, (ii) nonuniform samples due to clumping effect of Mtc and (iii) the absence of target gene sequences for IS6110 -PCR. Culture negativity, on the other hand, was likely to be associated with nonviable Mtc . Amplicor PCR is promising for direct detection of Mtc . The IS6110 -PCR, however, may not be as suitable because of possible existence of IS6110- deleted Mtc strain in Singapore.     

Evaluation of the Idaho Technology LightCycler PCR for the direct detection of Mycobacterium tuberculosis in respiratory specimens.

SETTING: The rapid detection of Mycobacterium tuberculosis (TB) in clinical samples is an important goal. The LightCycler heralds an advance in thermal cycle technology combining rapid cycle DNA amplification with fluorimetry, eliminating the need to perform amplification and product analysis separately. OBJECTIVES: To evaluate the LightCycler for direct detection of M. tuberculosis complex in respiratory specimens. To evaluate a DNA extraction method based on Chelex 100 resin, heating and ultrasonication for the prevention of endogenous inhibitions in respiratory samples. DESIGN: DNA was extracted from sputum samples using the Chelex method and polymerase chain reaction (PCR) for TB performed with the LightCycler. RESULTS: For 88 sputum samples positive by microscopy and culture for M. tuberculosis, 95% were PCR-positive. None of the five sputum samples that were smear-negative but culture-positive for M. tuberculosis, the 79 culture-negative sputum samples and the 29 sputum samples that were culture-positive for mycobacteria other than TB yielded positive PCR results. PCR inhibitors were not detected in any of the samples. CONCLUSION: The LightCycler proved a simple, reproducible and rapid system, reducing the time to result from weeks (culture) or days (conventional PCR) to hours. The Chelex 100 resin method produced good results for the smear-positive specimens. However, a larger study is required to determine the efficacy of the method with smear-negative specimens and for specimens known to contain endogenous inhibitors.     

The relative frequency of Mycobacterium tuberculosis and Mycobacterium avium infections in HIV positive patients, Ahvaz, Iran

ObjectiveTo estimate the prevalence of Mycobacterium tuberculosis (M. tuberculosis) and Mycobacterium avium (M. avium) infections in HIV-positive patients suspected to have pulmonary and extrapulmonary mycobacterial co-infection using PCR technique.MethodsTotally 50 samples comprising sputum, pleural fluid and CSF taken from HIV positive patients suspected to have mycobacterial infection, were processed. The demographic information and results of acid fast staining and culture were recorded for each patient. The PCR for detecting of M. tuberculosis comprised of specific primers targeting IS6110 gene sequence. For detecting of M. avium, PCR with primers that amplifies the mig gene were used.ResultsFrom 50 samples processed, 45 were sputum (90%), 3 pleural fluid (6%) and 2 CSF (4%). In total, 8 (16%) were culture positive, 7 had positive acid fast staining (14 %) and 13 samples (26%) were positive using PCR technique. All the positive samples were sputum and belonged to patients with pulmonary infection. Of these, 9 were positive for M. tuberculosis (69.2%) and 4 were identified as M. avium (30.8%), which 2 out of 13 positive samples showed mixed infections by both mycobacteria.ConclusionsThe PCR shows the highest detection rate (26%) of mycobacteria compared with culture and acid fast staining. The majority of infections were with M. tuberculosis (18%) and this shows the importance of this mycobacterial co-infection in HIV positive patients in the region of study.     

Rapid and efficient detection of extra-pulmonary Mycobacterium tuberculosis by PCR analysis.

SETTING: The diagnosis of extra-pulmonary tuberculosis (EPTB) remains an important clinical problem, primarily because of the inadequate sensitivity of conventional bacteriologic methods for detecting Mycobacterium tuberculosis in extra-pulmonary specimens. OBJECTIVE: To evaluate whether a IS6110-based polymerase chain reaction (PCR) method can be utilized to detect M. tuberculosis in non-pulmonary specimens. DESIGN: Specimens from 286 Mexican patients with a presumptive clinical diagnosis of EPTB were prospectively examined by Ziehl-Neelsen staining, mycobacterial culture on L?wenstein-Jensen slants, and by PCR. The DNA for PCR was extracted by the buffer lysis method and phenol-guanidine thiocyanate-chloroform. Primers that amplify a 200 bp fragment from the insertion-like M. tuberculosis sequence element IS6110 were utilized. RESULTS: Our results demonstrate that this PCR method is highly specific (100%) for identifying M. tuberculosis from a variety of specimens including cerebrospinal fluid (CSF), pleural fluid, ascitic fluid, pericardial fluid, urine, and lymph node exudate. Moreover, the sensitivity of PCR for detecting M. tuberculosis in CSF (94%), pleural fluid (94%), ascitic fluid and other extrapulmonary specimens (93%) greatly exceeds the sensitivity of conventional smear and culture methods. CONCLUSION: These results demonstrate that PCR can be a highly specific and sensitive aid in the detection of M. tuberculosis from extra-pulmonary specimens.     

PCR指印技术对新疆结核病病原Bacter460液体培养标本进行菌株分型

以结核分枝杆菌特异插入序列IS6 110两端序列为模板 ,设计一对外向PCR引物进行PCR扩增 ,从而建立一种结核分枝杆菌的快速分子生物学分型技术 ,该试验的基础是利用IS6 110在结核分枝杆菌染色体DNA中反复重复且IS6 110序列之间相距较近 ,经PCR扩增呈现多条带型构成DNA指印。在对新疆结核病人的 31份液体培养标本的PCR检测呈现 6种指印 ,该PCR分型技术对结核分枝杆菌的分型所需时间短 ,不需细菌再培养 ,DNA纯化和酶切、萨瑟恩转印或核酸杂交等繁琐步骤。证明该法是一种快速、准确的鉴定与分型方法并可直接进行分子流行病学研究     

The usefulness of PCR amplification of the IS6110 insertion element of M. tuberculosis complex in ascitic fluid of patients with peritoneal tuberculosis

Background: The diagnosis of tuberculous peritonitis (TP) may be difficult and elusive. The present study was designed to demonstrate the diagnostic usefulness of a nested polymerase chain reaction (PCR) assay, specific for the IS6110 insertion element of M. tuberculosis complex, in patients with ascites who were suspected of having TP in order to achieve a more timely diagnosis and treatment. Methods: Three HIV-negative patients suffering from fever and ascites were evaluated for suspected TP. Specimens were obtained from ascitic fluid, bone marrow, and peripheral blood and analyzed by both conventional methods and nested PCR for the presence of bacilli. Response to antituberculous treatment was considered as the final criterion for diagnosis of peritoneal tuberculosis. Results: All three patients had an excellent response to antituberculous therapy. Our PCR-based protocol detected M. tuberculosis complex DNA in the ascitic fluid of all patients, whereas conventional methods failed to establish the disease. Furthermore, in one patient, M. tuberculosis was also detected in both bone marrow and peripheral blood. Conclusions: PCR amplification of the IS6110 sequence of M. tuberculosis complex in ascitic fluid is a useful tool when peritoneal tuberculosis is suspected. However, its validity still needs to be established.