Differentiation of slowly growing Mycobacterium species, including Mycobacterium tuberculosis, by gene amplification and restriction fragment length polymorphism analysis

Abstract

A two-step assay combining a gene amplification step and a restriction fragment length polymorphism analysis was developed to differentiate the Mycobacterium species that account for >90% of potentially pathogenic isolates and >86% of all isolates in clinical laboratories in the United States. These species are M. tuberculosis, M. bovis, M. avium, M. intracellulare, M. kansasii, and M. gordonae. With lysates of pure cultures as the template, two oligonucleotide primers that amplified an ~1,380-bp portion of the hsp65 gene from all 139 strains of 19 Mycobacterium species tested, but not from the 19 non-Mycobacterium species tested, were identified. Digestion of the amplicons from 126 strains of the six most commonly isolated Mycobacterium species with the restriction enzymes BstNI and XhoI in separate reactions generated restriction fragment patterns that were distinctive for each of these species, except for those of M. tuberculosis and M. bovis, which were not distinguishable. By including size standards in each sample, the restriction fragment profiles could be normalized to a fixed distance and the similarities of patterns could be calculated by using a computer-aided comparison program. The availability of this data base should enable the identification of an unknown Mycobacterium strain to the species level by a comparison of the restriction fragment pattern of the unknown with the data base of known patterns.