Broth tubes are tubes containing a liquid medium. A typical nutrient containing broth medium such as Trypticase Soy broth contains substrates for microbial growth such as pancreatic digest of casein, papaic digest of soybean meal, sodium chloride, and water. A mass of organisms is floating on top of the broth. The organisms appear as a general cloudiness throughout the broth. A mass of organisms appears as a deposit at the bottom of the tube.
Slant tubes are tubes containing a nutrient medium plus a solidifying agent, agar-agar.
The medium has been allowed to solidify at an angle in order to get a flat inoculating surface. Agar plates are sterile petri plates that are aseptically filled with a melted sterile agar medium and allowed to solidify. Plates are much less confining than slants and stabs and are commonly used in the culturing, separating, and counting of microorganisms. Single colonies of microorganisms on agar plates can be described using the terms found in Appendix A . Obligate aerobes are organisms that grow only in the presence of oxygen.