Penicillin is a broad-spectrum antibiotic classified as a Beta-Lactam. There are many varieties of natural penicillins, with many chemically-altered, “semi-synthetic” derivatives created to increase solubility, effectiveness, and avoidance of normal antibiotic resistance mechanisms. The natural source for the basis of all penicillins is several species from the fungal genus Penicillium.
Penicillin’s mode of action is interference with the synthesis of peptidoglycan for bacterial cell walls. Bacteria continually repair and grow their cells through peptidoglycan synthesis. When it is transported out to the “growing point” of the wall, the new peptidoglycan subunit must be added and cross-linked to produce strength. Beta-lactam antibiotics prevent cross-linking, producing weak cell walls that cannot contain the cell membrane and cell contents. Rupture of the cell membrane kills the cell.