Eliminate pneumococcal colonization by targeting intracellular acidification that promotes H2O2 production to enhance bacterial survival.

Streptococcus pneumoniae is an important human pathogen that causes severe threat to the lives of children under 5 years old and the elder. Colonization in the nasopharynx is the prerequisite for pneumococcal disease. However, few attentions have been paid to prevent pneumococcal disease by eliminating colonization. In this work, pneumococci were found to undergo methionine starvation in the nasopharynx. In the in vitro experiments, methionine starvation induces the cytoplasmic acidification of S. pneumoniae, which benefits bacterial survival. Intracellular acidification was also observed in pneumococci colonizing the nasopharynx. We found that increased intracellular lactate level under methionine starvation causes intracellular acidification. Surprisingly, intracellular acidification elevates intracellular level of H2O2, a metabolite commonly considered harmful for bacteria, to enhance bacterial survival under methionine starvation. H2O2 inhibits bacterial autolysis that can be induced by methionine starvation to enhance bacterial survival. To impair pneumococcal survival and colonization, sodium oxamate was used as a drug by elevating intracellular pH through inhibiting lactate production. Interestingly, we found that penicillin alone could not impair pneumococcal survival and colonization efficiently due to the inhibited killing by intracellular acidification. However, the combination of sodium oxamate and penicillin not only killed bacteria effectively, but also almost eradicated pneumococcal colonization. To the best of our knowledge, it is the first time that H2O2 production was reported to be induced by intracellular acidification to benefit bacterial survival. Besides, sodium oxamate was found to be a novel drug for eradicating pneumococcal colonization by targeting intracellular acidification, particularly in the combination with penicillin.