The salvage pathways used in microorganisms differ from those of mammals. Some pathogens, such as the yeast "Candida glabrata" and the bacterium "Haemophilus influenzae" are NAD auxotrophs – they cannot synthesize NAD – but possess salvage pathways and thus are dependent on external sources of NAD or its precursors. Even more surprising is the intracellular pathogen "Chlamydia trachomatis", which lacks recognizable candidates for any genes involved in the biosynthesis or salvage of both NAD and NADP, and must acquire these coenzymes from its host.