Catalyzes the conversion of lactate to pyruvate (Potential). Contributes to S.aureus growth during nitrosative stress in both aerobically and anaerobically cultured cells, despite playing a secondary role in this resistance mechanism (By similarity). (S)-lactate + NAD(+) = H(+) + NADH + pyruvate Fermentation; pyruvate fermentation to lactate; (S)-lactate from pyruvate: step 1/1. Homotetramer. Belongs to the LDH/MDH superfamily. LDH family.