Introduction: The Mycobacterium tuberculosis complex includes the following species: Mycobacterium tuberculosis, Mycobacterium africanum, Mycobacterium bovis, Mycobacterium bovis-BCG, Mycobacterium microti, Mycobacterium caprae, Mycobacterium pinnipedii, and Mycobacterium canettii. These species cause tuberculosis in humans and animals. Identification of mycobacterial strains has classically been performed by phenotype study. Over the last years, laboratories have developed several molecular techniques to differentiate between these species. The aim of this study is to evaluate these methods and develop a simple, fast, identification scheme.
Material and methods: We analyzed 251 strains randomly obtained from the strains studied in 2004, and 797 strains received by the Reference Laboratory between 2005 and 2007. Phenotype characterization of 4183 strains isolated during that period was done by studying the colony morphology, characteristics in culture, nitrate reduction, niacin accumulation, and growth in the presence of thiophen-2-carboxylic acid hydrazide 10 microg/mL and pyrazinamide 50 microg/mL. The molecular identification scheme designed was as follows: 1) gyrB PCR-RFLP with RsaI, TaqI or SacII and hsp65 RFLP/PCR with HhaI., and 2) multiplex-PCR to determine the presence/absence of the RD9 and RD1 regions.
Results: The results showed 100% agreement between phenotype study and the molecular scheme.
Discussion: This molecular identification scheme is a simple and fast method, with 100% sensitivity and specificity, that can be implemented in most clinical laboratories at a low cost.