Virulence of clinical Mycobacterium tuberculosis strains in Lodz, Poland.

SETTING: The transmission of tuberculosis (TB) in the population and the development of disease are determined not only by the patient's immunological status, but also by the virulence of Mycobacterium tuberculosis strains. OBJECTIVE: To examine the virulence of M. tuberculosis clinical isolates with recognised transmission collected from 2006 to 2007 in a population in Lodz, Poland. METHODS: A total of 36 isolates were studied to determine their sensitivity to human neutrophil peptide 1 (HNP-1) and intracellular growth within THP-1 cells. Bacterial strains were cultured using HNP-1 at different concentrations. After incubation, the number of colony-forming units (cfu) was determined by bacteria plating. The intracellular survival was examined on days 3, 6 and 8 post-THP-1 infection by cfu enumeration. RESULTS: Overall, 69% of the isolates showed greater resistance to the highest HNP-1 concentration (15 g/ml) than the virulent H37Rv strain, and the growth of 10 strains was totally inhibited. On day 8, 56% of the strains displayed higher cfu numbers than the virulent H37Rv strain. CONCLUSION: The results suggest that isolates from our urban population represent highly virulent phenotypes. We could not find any significant difference in virulence between strains with unique genotypes and those in clusters.

Interactions between an M. tuberculosis strain overexpressing mtrA and mononuclear phagocytes.

PURPOSE: It was previously shown that the bacterial two-component regulatory signal transduction (2CR) system MtrAB may be associated with the ability of M. tuberculosis (Mtb) to survive in macrophages. In the present work Mtb mutants: Rv-78 with overexpression of mtrA and Rv-129 with elevated level of phosphorylation-defective MtrA were used for further investigation of the potential influence of the MtrAB system on Mtb interaction with human monocytes. MATERIAL/METHODS: Flow cytometry was used to determine the expression of MHC class II molecules. The expression of genes for inducible nitric oxide synthase (iNOS) and cathepsin G was quantified by RT-PCR. The association of Mtb strains with Rab5 and Rab7 positive vacuoles was investigated applying confocal microscopy. IL-10 and IL-12 secretion by monocytes as well as the Mtb susceptibility to cathepsin G were investigated. RESULTS: Mutation-carried and wild type Mtb strains inhibited MHC class II expression on monocytes to a similar extent. Monocyte stimulation with mycobacteria led to the increased production of IL-10 but no detectable amounts of IL-12 or NO were observed. Expression of the gene for iNOS was not detected while that for cathepsin G was shown, however its intensity was not associated with MtrA mutation. Mtb mutant strains were more effectively enclosed in phagosomes containing the late endosome marker Rab7 as compared to the control. CONCLUSIONS: The results may confirm the importance of the MtrAB system in mycobacterial capacity for successful survival in phagocytes, especially in the context of high degree of colocalization of Mtb Rv-78 to mature phagosomes.