HBD and necrotizing enterocolitis: Both strains were previously isolated from the fecal samples of patients who developed NEC.20,35,36 The hbd encodes a β-hydroxybutyryl-CoA dehydrogenase that catalyzes the early steps of the biosynthesis of n-butanol from acetyl-CoA, wherein acetoacetyl-CoA is reduced to 3-hydroxybutyryl-CoA that is responsible for the production of end-fermentation metabolites, including butyrate.37 At the genetic level, the hbd chromosomal disruption was confirmed; at the phenotypic level, hbd inactivation resulted in completely blocking the butyrate production without little effect on cell growth.