Establishing of a minimal set of tests (minimal standards) to identify species included in the genus Mycobacterium.

Mycobacterium genus includes over 100 species and subspecies; new species are discovered every year. Minimal standard criteria are represented by the resistance to acid-alcohol (e.g. in the Ziehl - Neelsen staining), the presence of some mycolic acids containing 60-90 carbon atoms that can be cleaved by pyrolysis in fatty acids with 22 - 26 carbon atoms and a guanine + cytosine content of the DNA of 61 to 71 mol %. The species with the highest rate of involvement are those from Mycobacterium tuberculosis complex, and tuberculosis is still one of the most widespread world diseases. The most important for a laboratory is to be able to identify the species from M. tuberculosis complex. We have done a series of experiments, their goal being to evaluate and establish a minimal set of useful tests for identification of mycobacterial species. We used strains from "Cantacuzino" Institute collection and applied a series of classical and modern methods. We appreciate that the minimal set of tests could be represented by the microscopic examination for acid-fast bacilli (AFB), the examination for the preferred growth temperature, the growth rate, the colonies morphology, pigmentation and photo reactivity, the niacin accumulation test, the test of nitrate reduction, the catalase test (in both variants), plus the susceptibility to Para-Amino Salicylic Acid, Para-Nitro-Benzoic Acid andto Tiophene-2-Carboxylic Acid Hydrazide.