Fig 1.
Schematic experimental procedure utilizing a modified Cornell-like mouse model.
Mice were infected with each MAC strain by aerosol route. Ten weeks after infection, mice were treated with clarithromycin and rifampicin for six weeks. At 28 weeks post-infection, which was 12 weeks after completion of chemotherapy, mice received immunosuppressants for 5 weeks as described in Materials and Methods. Mice were euthanized and lungs were collected for bacteriological and histopathological examination at the time points depicted by arrows.
Fig 2.
Reactivation of Mycobacterium avium complex in the lungs of mice following immunosuppression.
Mice were infected with approximately 500–1,000 CFUs of each MAC strain for 10 weeks and treated for 6 weeks with clarithromycin and rifampicin. Following the antibiotic regimen, mice were treated with immunosuppressants. A: MAV SM#1 represents the reactivation model of M. avium strains. B: MI SM#42 represents the reactivation model of M. intracellulare strains. Both graphs depict a dramatic decrease in bacterial counts, which were undetectable after antibiotic treatment and a dramatic increase after sulfasalazine treatment. For A and B, CFUs at 35 weeks represent the sulfasalazine-treated group. C and D represent the bacterial counts of individual murine lungs infected with MAV SM#1 and MI SM#42, respectively. Each group exhibited different reactivation levels according to the immunosuppressant used. The dashed line represents the detection limit of bacterial counts. Red arrows represent undetectable bacilli in each mouse. For A and B, the data are the median ± interquartile range (IQR).
Fig 3.
Regrowth of Mycobacterium avium complex in the lungs of mice following immunosuppression.
A: MAV104 and B: MAVSM#22 are the regrowth models of M. avium strains. C: MI ATCC13950 and D: MI SM#30 are the regrowth models of M. intracellulare strains. All graphs show a dramatic decrease in bacterial counts, although they remained detectable after antibiotic treatment with clarithromycin and rifampicin. The number of bacterial counts showed dramatic increase after dexamethasone and sulfasalazine treatment. The dashed line represents the detection limit of bacterial counts. The data are the median ± interquartile range (IQR). **P < 0.01 compared to no immunosuppression group. n.s., not significant.
Fig 4.
Lung inflammation values in mice.
Lung inflammation values are presented as the mean percentage of the area of inflammation from lung infection of five to six mice per group (±standard deviation). At 28 weeks and 35 weeks post infection, lung samples from each mouse were analyzed as described in the Materials and Methods. The inflamed areas were significantly increased after immunosuppression. *P < 0.05, ***P < 0.001, n.s., not significant.
Fig 5.
Histopathology of lungs in M. avium-infected mice.
A: MAVSM#1 represents the reactivation model and B: MAV104 and C: MAVSM#22 are the regrowth models of M. avium strains. (a) Untreated controls and (b) antibiotic-treated samples at 28 weeks post infection. Histopathological changes of lungs with M. avium infection at 35 weeks post infection with no immunosuppression (c), sulfasalazine treatment (d), and dexamethasone treatment (e). The scale bar represents 1 mm.
Fig 6.
Lung Histopathology of M. intracellulare infected mice.
A: MI SM#42 represents the reactivation model. B: MI ATCC13950 and C: MI SM#30 are the regrowth models of the indicated M. intracellulare strains. (a) Untreated controls and (b) antibiotic-treated samples at 28 weeks post infection. Histopathological changes of the lungs with M. intracellulare infection at 35 weeks post infection with no immunosuppression (c), sulfasalazine treatment (d), and dexamethasone treatment (e). The scale bar represents 1 mm at ×10 magnification.