At 6, 12, or 24 hr post-infection, pHrodo mean fluorescent intensity around PDIM- or ESX-1-mutant Mtb was significantly higher than around wild-type Mtb (Figure 6A), suggesting that phagosomes containing PDIM- or ESX-1-mutant Mtb becomes relatively more acidic than phagosomes containing wild-type Mtb. Here, ESX1 is linked to infection.