QUANTITATIVE CULTURE OF MYCOBACTERIUM-TUBERCULOSIS FROM CLINICAL SPUTUM SPECIMENS AND DILUTION END-POINT OF ITS DETECTION BY THE AMPLICOR PCR ASSAY

The minimum number of Mycobacterium tuberculosis CFU detectable in cli nical sputum specimens by the Amplicor PCR test was estimated by perfo rming the test on duplicate samples of quantitatively cultured serial dilutions of sputum. Positive PCR test results were obtained for all s amples that contained 42 CFU of M. tuberculosis. The detection limits of the PCR assay for decontaminated (N-acetyl-L-cysteine [NALC]-NaOH) and nondecontaminated (NALC only) specimens were equivalent, even thou gh the number of CFU cultured from decontaminated samples was only 11 to 20% of the number cultured from nondecontaminated samples. Thus, th e 42 CFU that could be detected in nondecontaminated specimens by the Amplicor PCR test correspond to the approximately 8 CFU (0.20 x 42) th at could be recovered in culture after decontamination with NALC-NaOH.