The impact of formate in Shigella flexneri after invading into HeLa cells

Shigellosis caused by Shigella is the one of the most important foodborne illness in global health, and the intracellular proliferation within the host cells is the most necessary step for inducing shigellosis. The known knowledge indicated that acetate was generated by the intracellular Shigella flexneri within the infected HeLa.

It meant that Shigella can utilize the cytosolic glucose as the energy source for its cytosolic proliferation. So, metabolites switching in cytosolic Shigella is a notable issue for preventing Shigella infection. In this study, we analyzed the turnover of 13C-glucose-derived metabolites among the mid-log phase Shigella, non-infected HeLa, and its Shigella-infected cells.

Briefly, the HeLa cells provided with uniformly-labeled [U-13C] glucose were infected with mid-log phase Shigella flexneri based on the gentamicin protection assay for 6-h. Meanwhile, each medium was collected every hour for following 1H- nuclear magnetic resonance (NMR) analysis. In addition, the intracellular bacteria within HeLa infected with either formate pre-treated Shigella or non-treated Shigella were counted for identifying the effect of formate on Shigella infection.

Our results showed that the 13C-acetate and 13C-formate were the two of the major products in mid-log Shigella. Otherwise, 13C-latctate and 13C-pyruvate were abundant in non-infected HeLa. However, when Shigella entered into HeLa the 13C-formate was gradually decreased after 2-h postinfection. In further, the intracellular bacterial number within HeLa after infection with formate pre-treated Shigella showed that formate can increase Shigella colonization in HeLa.

Our findings indicated that the intracellular Shigella cannot continually produce formate after invasion, and was also involved in regulation of Shigella infection. Our findings support that the glycolysis is important for Shigella infection, and one of the metabolites, formate, may play also an important role in pathogenesis.