TABLE 2.

Inactivation of M. tuberculosis H37Rv in centrally necrotizing granulomas by gamma irradiation of lung cryosections from M. tuberculosis-infected BALB/c IL-13^tg mice^a

Exposed dose (kGy)	TTP (days)	AFB, cord formationb
None	14 ± 1.3	+
0.24	16 ± 0.3	+
0.49	18 ± 1.2	+
0.98	17 ± 1.3	+
1.95	18c	+
5.85d	—e	—
11.71	—	—
17.56	—	—

^aBALB/c IL-13^tg mice were infected with 70 CFU of M. tuberculosis H37Rv, and at time points later than 100 days after infection, lung tissue biopsy specimens were isolated for subsequent preparation of cryosections. At least 3 slides, each containing 3 cryosections, were gamma irradiated at the indicated doses. After irradiation, sections were detached from the glass slides, whereby cryosections of each slide were pooled and homogenized in sterile water for subsequent inoculation of MGIT tubes. Inactivation of M. tuberculosis was evaluated by determining the TTP using the MGIT system, followed by microscopic detection of AFB and cord formation in cultures. TTP data are the mean ± SD.

^b+, positive for AFB and cord formation.

^cIrradiation eliminated M. tuberculosis in 3 out of 4 samples.

^dInactivation of M. tuberculosis was confirmed in 3 repeated experiments.

^e—, no mycobacterial growth or AFB.