Fig. 3: L-lactate protects H. pylori from complement-mediated elimination.

Overnight cultures of H. pylori PMSS1 WT or ∆lctP mutant with or without L-lactate supplementation overnight or for 1 h, as indicated, were treated by inactive and active serum for 1 h, and then viable bacterial CFUs were determined by plating. The survival percent was determined as described in Fig. 2. a Overnight cultures of H. pylori WT or ΔlctP mutant grown with the indicated concentration of L-lactate were treated by inactive and active 10% NHS. b Overnight cultures of WT H. pylori with 5mM L-lactate supplementation was treated by indicated percentage of NHS. c WT H. pylori cultures were treated with C57BL/6J mouse serum. d H. pylori cultures were treated by NHS only (gray bar), EGTA-conditioned NHS (white bar), C1q-depleted human serum (yellow bar), C2-depleted human serum (orange bar), Factor-B-depleted human serum (red bar), EGTA + Ca²⁺ (blue bar), or EGTA + Mg²⁺ (green bar) as in Fig. 2c. Survival ratio in the absence of L-lactate is identical to Fig. 2c. All tests were applied with 10% serum. e WT H. pylori cultures were treated with L-lactate for 1 h before exposed to NHS. In all panels, results were presented as survival percent \(\pm\) standard deviation (SD), and were derived from triplicate biological samples with a triplicate of each given sample. The p values were obtained by one-way ANOVA with Tukey’s multiple comparisons test (a, b, d), and a two-tail student t-test (c, e). The significance is indicated as * (p < 0.05), ** (p < 0.01), *** (p < 0.001), **** (p < 0.0001), or n.s. (not significant). Source data and exact p values are provided in the Source Data file.