Paratrophic Microorganisms

species of micro organisms that do not grow on synthetic nutrient media and that require for their development media containing blood, serum, protein hydrolysates, ascitic fluid, or other such substances of indefinite composition. Paratrophic microorganisms are usually pathogenic for man and animals.

Advances in the study of the physiology and biochemistry of microorganisms have made it possible in some cases to grow paratrophic microorganisms on very complex nutrient media containing, for example, a variety of amino acids, vitamins, and growth factors. The term “paratrophic microorganisms” has therefore become somewhat obsolete. However, certain pathogenic parasitic forms, such as rickettsiae, mycoplasmas, and the causative agent of syphilis, Spirochaeta pallida (Treponema pallidum), continue to be difficult, if not impossible, to grow in the laboratory on artificial nutrient media.