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.

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.

IS1607, a single-copy insertion sequence-related element of the Mycobacterium tuberculosis complex.

The species specificity of IS1607, a new Mycobacterium tuberculosis complex insertion sequence-related element, was investigated. IS1607 was present as a single copy in M. tuberculosis, M. bovis and M. bovis BCG strains. This sequence also existed in M. africanum and M. microti, but was not present in 69 strains of 19 atypical mycobacterial species analyzed by using polymerase chain reaction (PCR) or Southern hybridization assay. IS1607 appears to be specific for the M. tuberculosis complex.

Molecular characterisation of streptomycin-resistant Mycobacterium tuberculosis strains isolated in Poland.

Primary drug resistance of Mycobacterium tuberculosis strains in Poland increased two-fold between 1997 and 2000. Among 3705 drug-resistant strains investigated in 2000, 169 were resistant to streptomycin alone or in combination with isoniazid, rifampicin and/or ethambutol. The molecular basis of streptomycin resistance for 88 (52%) of these strains in comparison with 15 susceptible controls was determined. The most prevalent mutation was the single substitution Lys43Arg in the rpsL gene, found in 30.7% of the strains analysed. However, as many as 51% of the strains investigated carried no mutation in the rpsL or rrs genes. The multiple mutations present in two Beijing family strains were also identified.

Molecular epidemiology of drug-resistant Mycobacterium tuberculosis strains isolated from patients with pulmonary tuberculosis in Poland: a 1-year study.

OBJECTIVE: To characterise drug-resistant Mycobacterium tuberculosis strains isolated in Poland and to estimate the amount of recent transmission in the population. DESIGN: M. tuberculosis strains isolated from 251 patients with resistant pulmonary tuberculosis in Poland in 2000 were analysed by spoligotyping and IS6110 DNA fingerprinting. Part of the strains was also characterised by sequencing of the rpoB, katG and/or the regulatory region of the inhA gene. RESULTS: Using combined spoligotyping/IS6110-RFLP defined clusters, 29% of the strains were clustered, suggesting possible recent transmission. In some cases, transmission links among strains in clusters could be confirmed by epidemiological data and in addition, for most of the strains, by analysis of the mutations associated with resistance to rifampicin and/or isoniazid. Younger age, sex, immigration and history of previous treatment were not associated with clustering, whereas multidrug-resistant disease was more likely to cluster. Strains of the Beijing family could also be found in Poland, although with a much lower frequency than in the neighbouring countries. CONCLUSION: Transmission of drug-resistant M. tuberculosis strains was demonstrated, which might contribute to the emergence of drug-resistant tuberculosis in Poland.

DNA fingerprinting as an indicator of active transmission of multidrug-resistant tuberculosis in Poland.

OBJECTIVES: To use genetic fingerprinting to investigate the epidemiology of tuberculosis (TB) caused by Mycobacterium tuberculosis in Poland, a country with a relatively high incidence of tuberculosis, to improve TB control. DESIGN: One hundred M. tuberculosis isolates from 98 patients in the Institute of Tuberculosis and Lung Diseases in Warsaw from 1993 to 1995 and 85 isolates obtained from 50 patients in the Hospital of Lung Diseases in Lodz in 1996 were subjected to DNA restriction fragment length polymorphism (RFLP) analysis, using the insertion sequence IS6110 as a probe. RESULTS: IS6110-associated banding patterns of the M. tuberculosis isolates originating from different localities varied considerably, but isolates from Lodz had a higher degree of similarity. Strains with identical RFLP types were identified in patients of the same family or patients living in the same area, indicating active transmission. Of strains isolated in Warsaw, 45% were resistant to at least one drug, and 35% were resistant to two or more drugs and were classified as multidrug-resistant (MDR). Some drug-resistant isolates were found to have identical banding patterns and originated from epidemiologically linked cases. CONCLUSIONS: Active transmission of TB, including MDR TB, is occurring in Poland. Active measures must be taken to prevent the spread of drug-resistant TB in Poland and potentially, the rest of Europe.

Development of a new ligation-mediated PCR method for the differentiation of Mycobacterium tuberculosis strains.

BACKGROUND: There is a need for rapid, inexpensive methods for analysing a limited number of Mycobacterium tuberculosis strains. The ligation-mediated polymerase chain reaction (LM-PCR) method appears to be sufficiently discriminative and reproducible to be considered as a molecular tool for the initial evaluation of hospital outbreaks, laboratory cross-contamination, and family or small community transmission. OBJECTIVE: To develop a new LM-PCR method based on PCR amplification of the 5'-flanking region of insertion sequence (IS) 6110 consisting of SalI/PvuII digestion of chromosomal DNA, ligation of a SalI linker and differentiation of IS6110-carrying restriction fragments by suppression subtractive hybridisation. DESIGN: The fast ligation amplification polymorphism (FLAP) method was applied in the analysis of 62 M. tuberculosis clinical isolates and compared with IS6110-restriction fragment length polymorphism (RFLP) and mycobacterial interspersed repetitive units-variable number of tandem repeat (MIRU-VNTR) analyses of the same strains. RESULTS: The sensitivity of FLAP was estimated at 0.25 ng/l. FLAP yielded 32 patterns among the 62 M. tuberculosis strains compared to respectively 28 and 36 patterns obtained using MIRU-VNTR and IS6110-RFLP. Its Hunter-Gaston discriminatory index value (0.973) is similar to that of MIRU-VNTR (0.966) and IS6110-RFLP (0.971). The specificity of the FLAP patterns was also confirmed. CONCLUSION: FLAP proved highly discriminating, sensitive and specific and could be a valuable molecular tool, especially for analysing a limited number of M. tuberculosis strains.

Methods of introduction of foreign DNA into mycobacteria.

Two methods: triparental conjugation and electrotransformation were used for introduction of plasmid DNA into mycobacterial cells. The introduction of shuttle plasmid pMY10 into M. fortuitum mutant caused the activation of its chromosomal cryptic KmR gene. The used of integration vector pUS 903 allowed to obtain a collection of mutants interesting for studies of genetic determination of steroid biotransformation and drug-resistance in mycobacteria.

Postselective (directed) mutagenesis of fast-growing strain of Mycobacterium vaccae as a method of creating mutants showing changed phenotypic properties.

Postselective (directed) mutagenesis was used to create mutants of M. vaccae B3805 showing changed abilities for steroid biotransformations. Three morphological classes of such mutants, differing in colony colour: yellow, white and pink, were selected. Some of them can be helpful in genetic studies of steroid biotransformation. Two mutants were also shown to be hosts for foreign DNA.

IS990, a new species-specific insertion-sequence-related element of the Mycobacterium tuberculosis complex.

The structure and distribution of 1S990, a new Mycobacterium tuberculosis DNA sequence with homology to characterized insertion sequences (ISs), were investigated. IS990 was related to IS elements of the IS3 family and was present as a single copy in all 21 investigated M. tuberculosis strains, two Mycobacterium bovis strains and two M. bovis BCG strains. The sequence appears to be specific for the M. tuberculosis complex. The element carries two frameshift mutations and appears to be defective.