Nicotinamide adenine dinucleotide (NAD) has important biological functions in all living organisms. In its reduced form (NADH), it is an electron donor for many enzymes, including dehydrogenases of the respiratory chains. In Gram-positive bacteria, it is also a signal to alert the cell to a dangerous metabolic disfunction. This dysfunction can lead to a cell growth arrest. In the team, we are interested in its role in Streptococcus agalactiae, an opportunistic pathogen of animals and humans. Asymptomatic colonizer of its hosts, it can shift to a virulent state leading to various pathologies including septicemia and meningitis. The roles of NAD(H) on activity of two oxidases (Nox2 and a respiratory chain) and on the activity of the transcriptional regulator Rex will be presented in in vitro and in vivo (animal model) contexts.