Biological properties of M. Tuberculosis W cluster strains

: To study the biological characteristics of M. tuberculosis W cluster strains, the authors carried out in vitro, ex vivo, and in vivo experiments on 18 clinical strains and 2 laboratory ones, which had been clustered by a standardized methodology. Comparison was made in experiments in vitro and in macrophageal inoculation (ex vivo) from the 5,6-[3H]-uracil incorporation that reflected mycobacterial replication. The in vivo experiments estimated mycobacterial survival and cultivation and the lung pathomorphological pattern of infected animals. The results showed that M. tuberculosis W cluster strains had in vitro the mean multiplication rate, showing a high viability in the macrophages; the in vivo experiments demonstrated that the W cluster strains did not differ in virulence and might be both more and less virulent than the laboratory strain H37Rv. Notwithstanding the fact that the assumption on the hypervirulence of M. tuberculosis W cluster has not been supported, the distinguishing characteristic of the strains of this cluster is their enhanced capacity to survive in the macrophages no matter what infective dose.