FIG 4 .

Polyphosphate accumulation contributes to M. tuberculosis phenotypic tolerance to isoniazid and stress resistance. (A) Logarithmically growing ppx2 knockdown and empty vector control strains were incubated with isoniazid (10 µg/ml) for 7 days. The bacteria were plated on Middlebrook 7H10 agar with or without isoniazid (INH) (1 µg/ml) to determine the number of drug-sensitive and drug-resistant CFU. Data are the means of three independent samples, and the numbers are the numbers of CFU of isoniazid-resistant (gray bar) or isoniazid-sensitive bacteria (white bar) (*, P < 0.05; n = 3). (B to D) Logarithmically growing cultures of empty vector control and ppx2 knockdown strains were incubated under various stress conditions. The stress conditions were as follows: 40°C for 24 h (B), 0.05% SDS for 4 and 6 h (C), and acidified Middlebrook 7H9 broth (pH 4.5) (D). In panels B and C, the survival ratio is the number of surviving bacteria after challenge divided by the number of bacteria prior to incubation. Values are means ± SD. Values that are significantly different (P < 0.05) compared to the value for the empty vector control strain are indicated by an asterisk.