The Fluorescence In Situ Hybridization for Diagnosis of Mycobacterium tuberculosis Complex in Sputum Samples

Fluorescence In Situ Hybridization (FISH) assay has been a rapid, accurate and affordable method for detection of Mycobacterium tuberculosis complex (MTBC) in clinical isolates and lymph nodes of clinical samples. However, no performance data exist from sputum samples. The aim of this study was to develop the FISH assay for the simultaneous detection of MTBC in clinical isolates and sputum samples.

We identified the optimum conditions for the detection of MTBC by FISH in culture isolates. Then this approach was applied to detect 542 sputum samples from PTB suspects.

Among 542 cases, 45 (8.3%) had sputum samples that were positive for TB by BACTEC Mycobacteria Growth Indicator Tube 960 TB culture and the FISH technique. The sensitivity of the FISH assay was 97.1% for smear-positive samples and 36.4% for smear-negative samples compared with culture results, and according to clinical data, the sensitivity, specificity, and positive and negative predictive values of the FISH assay were 76.4%, 99.6%, 95.6%, and 97.6%, respectively, compared to 81.8%, 100%, 100%, and 98%, respectively, for culture and 63.6%, 98.6%, 83.3%, and 96%, respectively, for smears. Moreover, the estimated cost of FISH was only $3-$5 per test.

The FISH assay is accurate and affordable method for the detection of MTBC and may be an alternative to fluorescent smear as an effective method for detecting MTBC.