Iowa State University Veterinarian

Document Type



There are many factors to consider when deciding upon antimicrobial therapy. Some of them are suspected etiology, host status, organ system affected, and the properties of the drug being considered. Microbicidal drugs, such as penicillin, are superior to bacteriostatic drugs in immunosuppressed patients, severe and/or overwhelming infections where rapid action is required, and for long-standing infections to eliminate the pathogen, preventing carrier states or relapses. Due to the thick cell wall of bacteria and their capability of concentrating solutes, bacteria have a high intracellular osmolality. Penicillin causes cell wall defects by inactivating bacterial transpeptidase, which prevents the maintenance of an osmolar gradient, causing formation of spheroblasts, cell lysis, and death. Many penicillins have been developed. They can be divided into; natural penicillins, semi-synthetic penicillins such as penicillinase-resistant penicillins, broad spectrum (amino-) penicillins, and antipseudomonas and extended spectrum penicillins (See table one).