Catalyzes the dehydrogenation of acyl-coenzymes A (acyl-CoAs) to 2-enoyl-CoAs, the first step of the beta-oxidation cycle of fatty acid degradation. Is required for S.typhimurium to utilize medium- and long-chain fatty acids as sole carbon sources for growth. Is needed for bacterial survival during carbone-source starvation. a medium-chain 2,3-saturated fatty acyl-CoA + H(+) + oxidized [electron-transfer flavoprotein] = a medium-chain (2E)-enoyl-CoA + reduced [electron-transfer flavoprotein] a long-chain 2,3-saturated fatty acyl-CoA + H(+) + oxidized [electron-transfer flavoprotein] = a long-chain (2E)-enoyl-CoA + reduced [electron-transfer flavoprotein] Lipid metabolism; fatty acid beta-oxidation. Is under the negative control of the global regulator FadR and the positive control of the cAMP:cAMP receptor protein (cAMP:CRP) as well as the alarmone ppGpp. Is induced under carbon-source starvation and in the presence of the long-chain fatty acid oleate. Induction during carbon starvation is cAMP:CRP-dependent and sigma(S)-independent. Cells lacking this gene show undetectable in vivo beta-oxidation levels, and are unable to grow on oleate or decanoate as a sole carbon and energy source, in contrast to the wild-type parent strain. Belongs to the acyl-CoA dehydrogenase family.