FIG 5.

S. pneumoniae (Spn) contact-mediated killing of S. aureus (Sau) requires enzymes SpxB and LctO. (A) Oxidation of pyruvate to acetyl∼P by the enzyme pyruvate oxidase (SpxB). The reaction uses molecular O₂ and inorganic phosphate (P_i), producing CO₂ and H₂O₂ (circled). Acetyl∼P is then converted to acetyl coenzyme A by acetate kinase (AckA) in a reaction that produces ATP. The enzyme lactate oxidase (LctO) catalyzes the formation of pyruvate from lactate, producing H₂O₂. (B) S. pneumoniae strains TIGR4, TIGR4 ΔlctO, TIGR4 ΔspxB, and TIGR4 ΔspxB ΔlctO were inoculated on blood agar plates at the densities indicated on the right (CFU per milliliter) concurrently with S. aureus strain Newman, which was inoculated at a density of ∼10⁷ CFU/ml. (C) S. pneumoniae strains were inoculated at the densities shown at the top concurrently with S. aureus strain NRS049, inoculated at ∼10⁷ CFU/ml. The agar plates were incubated overnight at 37°C.