[Use of DNA probes labelled with radioisotopes in the mycobacteria laboratory]

We have studied 540 mycobacterial strains isolated in Lowestein-Jensen medium and 133 samples of different pathologic products against commercialized 125I-DNA Mycobacterium tuberculosis complex, Mycobacterium avitum-intracellulare and Mycobacterium gordonae. The sensitivity, specificity and positive and negative predictive values against isolated strains was 100% for the 3 studied probes. The 125I-DNA probe specific for M. tuberculosis complex is studied in samples with positive bacciloscopy; statistic values vary according to the cutting point of the different percentages of hybridization: at 1.5% the sensitivity, specificity and predictive negative and positive values are 38.6%, 71.4%, 97.5%, and 9.4% respectively, while if the cutting point percentage is 3% these values are: 33.1%, 100%, 100%, and 7.8% respectively. We believe that with these probes the identification time is limited to time needed for the incubation of prime cultures, and in some cases it can be performed on the day the samples reach the laboratory.