Inhibitory effect of sodium dodecyl sulfate in detection of Mycobacterium tuberculosis by amplification of rRNA

Evaluation of BacT/Alert 3D liquid culture system for recovery of mycobacteria from clinical specimens using sodium dodecyl (lauryl) sulfate-NaOH decontamination

A total of 52 mycobacterial isolates were recovered from 1,197 clinical specimens decontaminated by a sodium dodecyl (lauryl) sulfate (SDS)-NaOH protocol. Of these, 94% were recovered with the BacT/Alert 3D system (Organon Teknika, Durham, N.C.) and 79% were recovered on Löwenstein-Jensen (LJ) medium. Mean times to detection of organisms of the Mycobacterium tuberculosis complex (n = 47) were 22.8 days with LJ medium and 16.2 days with the system. The BacT/Alert 3D system is a rapid and efficient detection system which can be used with an SDS-NaOH decontamination procedure.

Multicenter evaluation of the fully automated COBAS AMPLICOR PCR test for detection of Chlamydia trachomatis in urogenital specimens

The fully automated COBAS AMPLICOR CT/NG test for the detection of Chlamydia trachomatis was evaluated in a multicenter trial. Test performance was evaluated for 2,014 endocervical swab and 1,278 urine specimens obtained from women and for 373 urethral swab and 254 urine specimens obtained from men. Culture served as the reference test. Culture-negative, COBAS AMPLICOR-positive specimens that tested positive in a confirmatory PCR test for an alternative target sequence within the C. trachomatis major outer membrane protein gene were resolved as true positives. The overall prevalence of chlamydia was 4.3% in cervical swabs and 11.0% in urethral swabs from men. When the results for each specimen type were considered separately, the resolved sensitivities were 96.5% (83 of 86) for endocervical swab specimens, 95.1% (39 of 41) for urine specimens from women, 100.0% (41 of 41) for urethral swab specimens from men, and 94.4% (17 of 18) for urine specimens from men; the resolved specificities were 99.4% (1,912 of 1,924) for endocervical swab specimens, 99.8% (1,204 of 1,207) for urine specimens from women, 98. 5% (325 of 330) for urethral swab specimens from men, and 100.0% (236 of 236) for urine specimens from men. For the subset of patients from whom both swab and urine specimens were collected, the combined results for both specimen types were used to identify all infected patients. Using these combined reslts as criteria, the resolved sensitivities for the COBAS AMPLICOR test were 82.6% (38 of 46) for endocervical swab specimens, 84.4% (38 of 45) for urine specimens from women, 84.2% (16 of 19) for urethral swab specimens from men, and 89.5% (17 of 19) for urine specimens from men. In comparison, the sensitivity of culture was only 56.5% (26 of 46) for endocervical specimens and 63.2% (12 of 19) for urethral specimens from men. The internal control provided in the COBAS AMPLICOR test revealed that 2.9% of specimens were inhibitory when they were initially tested. Nevertheless, valid results were obtained for 99. 1% of specimens because 68.7% of the inhibitory specimens were not inhibitory when a second aliquot of the original sample was tested. Two additional COBAS AMPLICOR-positive specimens were detected by retesting inhibitory specimens. The COBAS AMPLICOR CT/NG test for the detection of C. trachomatis exhibited equally high sensitivities and specificities with both urogenital swab and urine specimens and, thus, is well-suited for use in screening.

LCx: a diagnostic alternative for the early detection of Mycobacterium tuberculosis complex

This study aims to evaluate the performance of a new diagnostic method (LCx Tuberculosis Assay, Abbott Laboratories) based on Ligase Chain Reaction (LCR) technology, for the detection of Mycobacterium tuberculosis in respiratory and non-respiratory specimens and compare it with standard microbiological data and the clinical diagnosis of tuberculosis. Nine hundred specimens were collected from patients with a high suspicion of tuberculosis (740 respiratory samples and 160 non-respiratory specimens). The study was divided into two separate groups: samples washed and distilled water (207 samples) and unwashed samples that were directly resuspended in phosphate buffer (693 samples). The overall sensitivity, specificity, positive and negative predictive values of samples washed with distilled water after decontamination with SDS-NaOH were: 54%, 100%, 100%, and 94%, respectively. If these results were divided according to origin of specimens, the sensitivity, specificity, positive and negative predictive values in respiratory and non-respiratory samples were 54.5%, 100%, 100%, 94% and 50 100%, 100%, 93%, respectively. In contrast, for the non-washed samples, values were 85%, 95%, 80% and 98%, respectively. Respiratory and non-respiratory samples gave values of 84%, 96%, 77%, and 97.5% versus 89%, 99%, 94%, and 98%. The LCx M. tuberculosis assay is a novel, semi-automated assay and a rapid and highly specific technique for screening all forms of tuberculosis, including non-respiratory forms.

Clinical application of the Mycobacterium tuberculosis direct test: case report, literature review, and proposed clinical algorithm

The relatively new Mycobacterium tuberculosis direct test (MTDT) enzymatically amplifies M tuberculosis complex 16s ribosomal RNA. The sensitivity of the test ranges from 75 to 100%, with specificity of 95 to 100%, positive predictive value between 78% and 100%, and negative predictive value between 95% and 100%. Similar test characteristics have been documented in nonrespiratory specimens and in specimens that ultimately grow nontuberculous mycobacterium (NTM). This test allows for rapid identification of M tuberculosis in the smear-positive patient and may greatly improve sensitivity over acid-fast bacilli smear alone. A negative test result with a positive smear suggests infection with NTM or Mycobacterium avium complex. We present a case that illustrates the value of MTDT for analysis of tissue specimens in immunocompromised patients with suspected mycobacterial disease and review the rapidly developing literature about this test. We propose an algorithm using MTDT, acid-fast smear, and mycobacterial culture for the diagnosis and treatment of the immunocompromised patient with suspected mycobacterial infection.

Rapid diagnosis of extrapulmonary tuberculosis by ligase chain reaction amplification

A rapid amplification-based test for the diagnosis of extrapulmonary tuberculosis, the LCx Mycobacterium tuberculosis Assay from Abbott Laboratories, was evaluated. Results from the LCx M. tuberculosis Assay were compared with those from culture and the final clinical diagnosis for each patient. A total of 526 nonrespiratory specimens from 492 patients were tested. The specimens included urine; feces; lymph node exudates; pleural, cerebrospinal, articular, and ascitic fluids; tissue biopsies; gastric aspirates; purulent exudates; blood; and bone marrow aspirates. After combination of the culture results and the patient's clinical data, a total of 135 specimens were collected from 122 patients with a diagnosis of extrapulmonary tuberculosis. The sensitivity, specificity, and positive and negative predictive values for the LCx M. tuberculosis Assay were 77.7, 98.7, 95.2, and 93.1%, respectively; these values rose in resolved cases of TB to 78.5, 100, 100, and 93.1%, respectively. For 37 (27.4%) specimens from patients smear positive for the disease and 98 (72.6%) specimens from patients smear negative for the disease, the sensitivities of the LCx M. tuberculosis Assay were 100 and 71.1%, respectively. Statistically significant differences (P < 0.01) in sensitivities were found between culture and the LCx M. tuberculosis Assay. These differences were even greater among smear-negative specimens. The results demonstrate that the LCx M. tuberculosis Assay will provide rapid and valuable information for the diagnosis of extrapulmonary tuberculosis.

An internal control for routine diagnostic PCR: design, properties, and effect on clinical performance

We constructed internal controls (ICs) to provide assurance that clinical specimens are successfully amplified and detected. The IC nucleic acids contain primer binding regions identical to those of the target sequence and contain a unique probe binding region that differentiates the IC from amplified target nucleic acid. Because only 20 copies of the IC are introduced into each test sample, a positive IC signal indicates that amplification was sufficient to generate a positive signal from targets present at the limit of test sensitivity. The COBAS AMPLICOR Chlamydia trachomatis, Neisseria gonorrhoeae, Mycobacterium tuberculosis, and human hepatitis C virus tests exhibited inhibition rates ranging from 5 to 9%. Approximately 64% of these inhibitory specimens were not inhibitory when a second aliquot was tested. Because repeatedly inhibitory specimens were not reported as false negative and because additional infected specimens were detected during retesting, test sensitivities were 1 to 6% greater than they would have been if the IC had not been used.

Detection and identification of mycobacteria by amplification of RNA and DNA in pretreated blood and bone marrow aspirates by a simple lysis method

A sodium dodecyl (lauryl) sulfate method was evaluated for the preparation of blood specimens and bone marrow aspirates for use in two amplification procedures (Gen-Probe Amplified Mycobacterium Tuberculosis Direct Test [AMTDT] and Roche Amplicor M. avium/M. intracellulare [MAI] Test) for the detection and identification of Mycobacterium tuberculosis and M. avium and M. intracellulare, respectively. The AMTDT is based on amplification of rRNA, whereas the Amplicor MAI Test amplifies a specific DNA region of the 16S rRNA gene. The results of amplification techniques were compared with those of standard culture and culture in BACTEC 13A and BACTEC 12B liquid media. A total of 121 blood specimens and 15 bone marrow aspirates were collected from 136 AIDS patients. Mycobacterial growth was recovered for 103 specimens; 35 yielded M. tuberculosis, 62 yielded M. avium, 5 yielded M. genavense, and 1 yielded M. kansasii. The values of sensitivity and specificity in pretreated specimens for detection of M. tuberculosis by the AMTDT were 94.3 and 100%, respectively, and those for detection of M. avium by the Amplicor MAI Test were 91.9 and 100%, respectively. The simple lysis method described in the present work allows the recovery of mycobacteria from blood specimens and bone marrow aspirates and may be used in combination with the AMTDT and the Amplicor MAI Test to detect and identify different members of the genus Mycobacterium. This method might also be applicable for the identification of mycobacteria from blood culture fluids with acridinium-ester-labeled DNA probes.

Evaluation of the semiautomated Abbott LCx Mycobacterium tuberculosis assay for direct detection of Mycobacterium tuberculosis in respiratory specimens

Five hundred twenty processed respiratory specimens from 326 patients received for the diagnosis of tuberculosis or other mycobacterial infections were tested by means of the LCx Mycobacterium tuberculosis Assay from Abbott Laboratories, which uses ligase chain reaction technology for the direct detection of M. tuberculosis complex in respiratory specimens. The results of the LCx M. tuberculosis Assay were compared with the results of culture and staining techniques. After a combination of culture results and the patient's clinical data, a total of 195 specimens were collected from 110 patients who were positively diagnosed as having pulmonary tuberculosis. Twenty-three of these 195 specimens which corresponded to 10 patients with a history of pulmonary tuberculosis (TB) and anti-TB treatment ranging from 1 to 6 months were culture negative. The other 172 specimens were culture positive for M. tuberculosis. With an overall positivity rate of 37.5% (195 of 520 specimens), the sensitivity, specificity, and positive and negative predictive values were 90.8, 100, 100, and 94.7%, respectively, for the LCx M. tuberculosis Assay; 88.2, 100, 100, and 93.4%, respectively, for culture; and 82.6, 92, 72.9, and 97.6%, respectively, for acid-fast staining. For 161 specimens (82.6%) from patients smear positive for the disease and 34 specimens (17.4%) from patients smear negative for the disease, the sensitivity values for the LCx M. tuberculosis Assay were 98.8 and 53%, respectively. There were no statistically significant differences in the sensitivities and specificities between the LCx M. tuberculosis Assay and culture (P > 0.05). Conclusively, the LCx M. tuberculosis Assay has proved to have an acceptable sensitivity and a high specificity in detecting M. tuberculosis and has the potential of reducing the diagnosis time to an 8-h working day.