FIG 9.

DprA involvement in Streptococcus pneumoniae virulence and pathogenicity. Streptococcus pneumoniae D39 (WT) and ΔdprA mutant were used to evaluate bacteremia and acute pneumonia in CD1 mice. (A) For the bacteremia mouse model, 1 × 10⁴ CFU bacteria were injected intraperitoneally. After 24 h, spleens were isolated from euthanized mice, homogenized dilutions were plated, and pneumonia burdens were calculated. (B) For the acute pneumonia mouse model, animals were anesthetized using isoflurane and intranasally administered 5 × 10⁶ CFU pneumococci. After 48 h, mice were euthanized, lungs were removed, and bacterial burdens were calculated. The competitive index (CI) is the ratio of mutant versus wild type in the output sample divided by the input ratio of mutant versus wild type provided in the sample. A CI of >0.7 is defined as attenuated. (C) DprA is required to shut off competence and regulate ~100 “early” and “late” competence genes. Overexpression of early and late competence genes causes cellular stress and excess energy consumption (energy-deprived condition) in dprA mutant. Here, ssbB (late competence gene) is translation-fused with firefly luciferase gene to generate translation fusion construct SsbB-luxABCDE and measure the overexpression of late competence gene after competence activation through the addition of CSP1. A ΔdprA mutant of S. pneumoniae cannot shut off the competence pathway activated by CSP1 addition, leading to more energy consumption and causing unwanted cellular stress and energy deprivation. The ΔdprA mutant is susceptible to low CSP1 concentration for prolonged competence activation (more light), resulting in overexpression of allolytic factors LytA, CbpD, and CibAB. It also induces the fratricide immunity protein ComM. Combined action of low energy and excessive overexpression of allolytic enzyme, followed by the release of pneumolysin, potentially leads to bacterial death and attenuated virulence.