There are dozens of different types of microbial growth media available to Microbiologists, developed for a wide variety of purposes. The USP references many of these to demonstrate the quality of both compounded drug products and the control of compounding environments. The various types of media serve specific purposes based on the goal of the test. This might include recovery of the broadest range possible of organisms in a sterility test, screening for a specific organism if it would be particularly dangerous in a certain dosage form, or capturing anything that might be in the compounding environment that might find its way into finished product. Microbial growth media can be prepared in both liquid and solid forms, depending on the application. Tryptic Soy Agar (TSA) and Tryptic Soy Broth (TSB), for example, have the same nutrient profile and similar ingredients, but TSA is a solid and TSB is a liquid. For conducting passive air sampling, for example, a solid TSA plate is easier to handle and leave out in the hood during compounding. Liquid media, like TSB, is generally better at growing organisms, and should be used where possible for recovery of microorganism in drug products. Liquid media is more conducive to growth, since nutrients, oxygen, and waste products move around more freely, and temperature is more uniform and constant in a fluid.