Protein tyrosine phosphatase PtpA is not required for Mycobacterium tuberculosis growth in mice

Abstract

Mycobacterium tuberculosis (Mtb) alters the host response to infection by secreting protein factors. Mtb produces two secreted protein tyrosine phosphatases, PtpA and PtpB, which are thought to interfere with host signaling. Deletion of ptpA or ptpB attenuates bacterial growth in activated macrophages. To address the in vivo function of PtpA, we generated a genetic deletion mutant, DeltaptpA. The mutant was not defective when grown in vitro, consistent with the presumed role of PtpA in the host. The ptpA mutant, however, also showed no growth defect in a mouse infection model. The absence of a growth defect in mice suggests that the requirement for PtpA differs in mouse and human infections, and that mice are not a suitable infection model for the study of PtpA.

Fig. 1

Chromosomal replacement of the ptpA gene with a hygromycin-resistance cassette by homologous recombination. Southern blot showing the correct insertion of the hygromycin cassette. (a) Recombination generates the predicted XbaI fragment of 3.2 kb in the ptpA deletion strain compared with the wild-type Erdmann parent. (b) A probe for ptpA generates a 2.6-kb fragment only in the parent. (c) A probe for the hygromycin-resistance cassette generates a 3.2-kb fragment only in the mutant.

Fig. 2

Growth of ptpA deletion strain compared with the parental wild-type Erdmann strain. (a) In vitro growth of wild-type Mtb and DptpA mutant in 7H9 medium. (b) CFU recovered from lungs of mice infected with wild-type Erdmann and ptpA mutant. (c, d) CFU recovered from spleen and liver. The ptpA deletion does not affect in vitro or in vivo growth of Mtb. Error bars indicate the SD of data from five animals.