24 research outputs found
Mycobacterium Bovis BCG disrupts the interaction of Rab7 with RILP contributing to inhibition of phagosome maturation.
Phagosomes containing M. tuberculosis and M. bovis BCG interact normally with early endosomes but fail to fuse with late endosomes and lysosomes. Whereas many early events of mycobacterial phagosomes have been elucidated, the exact mechanism of the inhibition of fusion with lysosomes is still unclear. Several Rab GTPase proteins were shown to be involved in membrane fusion and vesicular transport. In particular, Rab7 associates with the phagosomal membrane and regulates the fusion between late endosomes and lysosomes. This function of Rab7 was shown to be mediated in epithelial cell models by the Rab7 effector RILP (Rab7-interacting lysosomal protein). However, the relevance of Rab7-RILP interaction to phagosome biogenesis in macrophage infected with mycobacteria is still unknown. In this study, cotransfection of RAW 264.7 cells with Rab7 and RILP revealed that Rab7-RILP interaction occurs in macrophages ingesting latex beads. Thereafter, this cell system model was used to demonstrate that infection with live but not killed M. bovis BCG inhibited RILP recruitment despite Rab7 acquisition by the phagosome. Further investigation using immobilized RILP to pull down active Rab7 (GTP-bound form) from macrophage lysates demonstrated that inactive Rab7 (GDP-bound form) predominates in cells infected with live BCG. In addition, cell-free system experiments demonstrated that BCG culture supernatant contains a factor that catalyzes the GTP/GDP switch on recombinant Rab7 molecules. Such a factor was shown to diffuse beyond BCG phagosomes and target other Rab7-positive compartments. These findings suggest that live mycobacteria express within the macrophage a Rab7 deactivating factor leading to abortion of RILP-mediated fusion with lysosomes
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Mycobacterium Abscessus Complex Infections Among Lung Transplant Recipients: A National Retrospective Cohort Study
Mycobacterium abscessus (MABS) is a non-tuberculous mycobacteria (NTM) known to cause life threatening disease involving the lung, skin and soft tissue, and disseminated disease in lung transplantation recipients (LTRs). Therefore, many centres consider the presence of MABS as a relative contraindication to lung transplantation (LT). The goal of this study was to assess the epidemiology and outcomes of MABS infection before and after LT in a pan-Canadian cohort.
We conducted a multicenter retrospective cohort study including all 4 LT centers in Canada. All LTRs transplanted between January 2006 and December 2016 with at least one respiratory sample positive for MABS complex prior to or post transplantation were included. Pulmonary disease was defined using the American Thoracic Society criteria for NTM lung infection. Follow up duration was 5 years after transplantation.
Among a cohort of 2230 LTRs across Canada, 15 patients (0.67%) had MABS infection prior to LT. Median age was 32 (range 17-58), 7/15 (47%) were female and the most common underlying disease was cystic fibrosis 11/15 (73%). Among patients with MABS infection pre-transplant, 80% (12/15) received treatment prior to transplant. Following LT, 53% (8/15) developed recurrent MABS infection (6 disease and 2 colonization). Five-year mortality among patients with pre-transplant MABS infection was 27% (4/15). Among patients with pre-transplant MABS infection, mortality was higher in those who had recurrence of MABS infection after transplant (50% vs 0%, 0.077), though this did not reach statistical significance. Microbiologic eradication prior to transplant occurred in 8/15 (72.7%) and was associated with decreased mortality (0% vs 57.1%, 0.026) and decreased risk of recurrence (12.5% vs 100%, 0.001). In addition to the 8 patients with recurrent disease, 12 patients developed de novo MABS infection after transplant of which 66.7% (8/12) had disease. Among the 14 patients with post-transplant disease, 5 year mortality was 50% (7/14), the majority of which was due to MABS infection (5/7, 71.4%).
MABS is an uncommon cause of infection among LTRs. Recurrence rate among those with pre-transplant infection is high and this may be associated with decreased survival. Survival among those with pre-transplant MABS infection was similar to contemporary cohorts of LTRs
Canadian Multicenter Laboratory Study for Standardized Second-Line Antimicrobial Susceptibility Testing of Mycobacterium tuberculosis â–¿
The purpose of this study was to establish a standardized protocol for second-line antimicrobial susceptibility testing of Mycobacterium tuberculosis using the Bactec MGIT 960 system in Canadian laboratories. Four Canadian public health laboratories compared the susceptibility testing results of 9 second-line antimicrobials between the Bactec 460 and Bactec MGIT 960 systems. Based on the data generated, we have established that the Bactec MGIT 960 system provides results comparable to those obtained with the previous Bactec 460 method. The critical concentrations established for the testing of the antimicrobials used are as follows: amikacin, 1 μg/ml; capreomycin, 2.5 μg/ml; ethionamide, 5 μg/ml; kanamycin, 2.5 μg/ml; linezolid, 1 μg/ml; moxifloxacin, 0.25 μg/ml; ofloxacin, 2 μg/ml; p-aminosalicylic acid, 4 μg/ml; rifabutin, 0.5 μg/ml