Early identification of Mycobacterium tuberculosis and Mycobacterium avium using the polymerase chain reaction on samples positive by a rapid commercial culture system.

A combination of two methods -- a rapid culture method [Mycobacteria Growth Indicator Tube (MGIT); Becton-Dickinson, USA] and a double polymerase chain reaction (PCR) assay -- was assessed for the detection and identification of Mycobacterium tuberculosis and Mycobacterium avium from clinical samples. The aim of the study was to evaluate the ability of the system to offer rapid and accurate diagnosis of mycobacterial infections. After decontamination, clinical samples (n = 554) were stained and cultured in parallel on solid media and in MGITs following standard procedures. The performance of the two culture systems was compared. Positive MGITs were tested for the presence of Mycobacterium tuberculosis and Mycobacterium avium by PCR of IS6110 (Mycobacterium tuberculosis) and the 16S rRNA gene (Mycobacterium avium). A total of 41 mycobacteria -- 27 Mycobacterium tuberculosis isolates, eight Mycobacterium avium isolates, and six other species of mycobacteria -- were isolated by one or both culture media. The MGIT system recovered 36 (87.8%) mycobacteria and the solid media 33 (80.4%). The mean time to detection by the two culture systems did not differ overall, but the mean time to detection of Mycobacterium avium from smear-positive specimens was shorter in MGITs than in solid media (5.25 days vs. 16.25 days, P < 0.05). The double PCR assay performed on the 36 positive MGITs correctly identified all 24 Mycobacterium tuberculosis-positive MGITs and all six Mycobacterium avium-positive vials. Therefore, application of the PCR assay to positive MGITs may mean that Mycobacterium tuberculosis and Mycobacterium avium can be identified at an earlier stage than with current methods.

Evaluation of the Abbott LCx Mycobacterium tuberculosis assay for direct detection of Mycobacterium tuberculosis complex in human samples.

Seven hundred thirty-seven clinical samples from 460 patients were processed for direct detection of Mycobacterium tuberculosis complex by a semiautomated ligase chain reaction commercial assay, the LCx Mycobacterium tuberculosis Assay (LCx assay) from Abbott Laboratories. Results were compared to those of direct microscopy and standard microbiological culture. Of 26 patients (5.7%) with a culture positive for M. tuberculosis, 22 (84.6%) were found positive by the LCx assay. The sensitivity of the LCx assay was 98% for smear-positive samples and 27% for smear-negative samples. With an overall culture positivity rate for M. tuberculosis of 8.3% (61 of 737 samples) and after resolution of discrepant results according to clinical data, the sensitivity, specificity, and positive and negative predictive values of the LCx assay were 78, 100, 95, and 98%, respectively, compared to 85, 100, 100, and 98%, respectively, for culture and 67, 99, 87, and 97%, respectively, for acid-fast staining. In conclusion, the LCx assay proved satisfactory and appears to be an easy-to-use 1-day test which must be used with standard culture methods but can considerably reduce diagnosis time versus culture. However, its clinical interest appears to be limited in our population with low mycobacterial prevalence because of its cost considering the small gain in sensitivity versus direct microscopy.

About two cases of Mycobacterium simiae infection in AIDS: review of the pathogenicity.

Mycobacterium simiae is an ubiquitous species rarely involved as a cause of human infection. Its pathogenicity remains therefore unclear and controversial. Disseminated infections with M. simiae occur rarely and only 7 cases have been reported in patients with acquired immunodeficiency syndrome (AIDS). At least, two were mixed infections caused by M. simiae and M. avium-intracellulare. We report the case of two AIDS patients presenting with pure M. simiae infections: one was a disseminated infection and the other a pulmonary infection. Epidemiology and pathogenicity of M. simiae in pulmonary, extra-pulmonary and disseminated infections are reviewed.

Evaluation of the Gen-Probe amplified Mycobacterium tuberculosis direct test for the routine diagnosis of pulmonary tuberculosis.

A total of 624 respiratory specimens from 543 patients (418 Belgian, 110 Rwandan, and 15 Colombian patients) were tested for the presence of Mycobacterium tuberculosis by the Mycobacterium Tuberculosis Direct Test (MTDT, Gen-Probe). Compared to culture, the MTDT on 497 samples of sputum or broncho-alveolar lavage from Belgium had a sensitivity, specificity and positive and negative predictive value of 86.4%, 96.0%, 50.0% and 99.3% respectively. The pooled results for Rwanda (112 specimens) and Colombia (15 specimens) were 97.8%, 65.7%, 88.2%, 92% respectively. After resolution of discrepant results by taking into account the clinical data, the results for the Belgian patients were 86.9%, 96.2%, 52.6%, 99.3% respectively, and for the Rwandan-Colombian patients 98.1%, 100%, 100% and 92% respectively. Results could be improved by testing more than one specimen from each patient and the inclusion of an internal control to detect inhibitors of the reaction. Culture remains necessary for drug susceptibility tests and the isolation and identification of non-tuberculous mycobacteria.

Mycobacterium simiae disseminated infection in a patient with acquired immunodeficiency syndrome.

Mycobacterium simiae is commonly found in nature and its role as a pathogen has been controversial. A case of disseminated M. simiae infection with blood, pulmonary and cutaneous localization is reported here. The pathogenic role of M. simiae was clearly demonstrated as it was the only organism isolated from sputum, broncho-alveolar lavage fluid, as well as blood and skin tissue. Identification of M. simiae by conventional testing may be difficult. Analysis of fatty and mycolic acid patterns, as performed in this case, is necessary to confirm its identification.