Mycobacterium tuberculosis cording in alveolar macrophages of patients with pulmonary tuberculosis is likely associated with increased mycobacterial virulence.

Mycobacterium tuberculosis (Mtb) is an infectious agent that causes tuberculosis (TB) in humans. A study of the volume of Mtb population and the detection of Mtb virulence in the lungs of patients with pulmonary TB are of great importance for understanding the infectious process and the outcome of the disease. We analyzed the functional state of Mtb and their number in alveolar macrophages obtained from the resected lungs of patients with TB in ex vivo culture and determined that the number of Mtb, referred mainly to the Beijing genotype family (A0 and B0/W148 clusters), were significantly different in cells between different patients. Only single Mtb were found in alveolar macrophages of some patients, while Mtb were actively replicated in colonies in alveolar macrophages of other patients, including cord morphology of Mtb growth (the indicator of Mtb virulence). Our data demonstrated association between the formation of Mtb cording in alveolar macrophages of patients and increased virulence of Mtb from the lungs of these patients in guinea pig TB model. The find of cording formation by replicating Mtb in human alveolar macrophages may be used for preliminary quick estimation of increased Mtb virulence in individual patients with pulmonary TB.