Q.What are antibiotics ?

Antibiotics are microbially-produced (or derived) chemical substances that selectively inhibit the growth of, or destroy, disease-causing microorganisms without significantly harming the host — penicillin, discovered by Alexander Fleming from the mould Penicillium notatum, is the archetypal example.

An antibiotic is a chemotherapeutic agent — originally defined as a substance produced by one microorganism (bacterium or fungus) that, even in very low concentration, either kills or inhibits the growth of another microorganism (typically pathogenic bacteria). Antibiotics work through various mechanisms, such as inhibiting bacterial cell-wall synthesis, protein synthesis, or nucleic-acid replication, and are broadly classified as bactericidal (kill bacteria, e.g. penicillin) or bacteriostatic (stop bacteria from multiplying, allowing the immune system to clear the infection, e.g. tetracycline). Penicillin, the first antibiotic to be widely used clinically, is produced by …