Relative susceptibilities of microbes to antimicrobial agents. Examples of the most resistant microbes are prions, bacterial endospores, mycobacteria, cysts of protozoa, etc. the basic principle of microbial control The action of antimicrobial agents. It alters cell walls and membranes; thus, cells burst due to osmotic pressure. Damage to the cell can be caused by extreme heat or certain chemicals, and radiation can damage protein and nucleic acid. Ideal Methods for Selection of Microbes. ? Inexpensive ? Fast-acting ? Stable during storage ? Capable of being harmless in the process of controlling microbial growth.