An antibiotic was originally a material created by one microorganism that selectively inhibits another’s development. Since then, synthetic antibiotics have been developed that perform comparable tasks, typically chemically similar to natural antibiotics. There are no effects of antibiotics on viral infections. Antibiotics are used to treat bacterial infections in humans and animals. Several proposed classifications of antibiotics including chemical structure, mode of action, or organism of inhibitory activity. Most of the classification systems include two primary categories, the first categorizing based on chemical structure and the second categorizing based on the mechanism of action. Depending on their action, antibiotics are classified into bactericidal or bacteriostatic agents. Bactericidal agents kill or destroy the bacteria in the infected tissue; examples of bactericidal agents include penicillin, cephalosporins, fluoroquinolones, and aminoglycosides. Bacteriostatic agents cease bacterial multiplication, allowing other mechanisms of the immune system to kill the microbes. The antibacterial actions of antibiotics include inhibiting the bacterial cell wall, interrupting protein synthesis, plowing down the bacterial nucleic acid (DNA/RNA), inhibiting the biochemical metabolism, chelating metallic cations that are necessary for bacterial growth, and impairing the bacterial membranes by disintegrating it.