Technically, an antibiotic is a substance that is produced by one microorganism and it is capable of killing or inhibiting the growth of another microorganism which can a virus, bacteria, fungi, yeast, protozoan or any other pathogen.
The first antibiotic that was developed was Penicillin, a biological compound that is produced by fungi in the genus Penicillium. It was discovered by Alexander Fleming in the year 1928. After that, several other types of antibiotics produced by different species of bacteria and fungi were isolated. Some of these include cephalosporins; aminoglycosides such as streptomycin, gentamicin and kanamycin; ansamycins such as geldanamycin and carabecephems; glycopeptides like vancomycin; macrolides like erythromycin and azithromycin, penicillin, quinolone, polypeptide and sulfonamide.
All these antibiotics have different mode of action by which they act as therapeutic agents. Some of the modes of action by different antibiotics are mentioned below:
Cell Wall Synthesis Inhibitors:
Bacteria contain murein or peptidoglycan that is highly essential in maintaining the cell wall structure. Cell wall synthesis inhibitors such as beta-lactams, cephalosporins and glycopeptides block the ability of microorganisms to synthesize their cell wall by inhibiting the synthesis of peptidoglycan.
Interfering with Protein Synthesis:
These classes of antibiotics inhibit the protein synthesis machinery in the cell. Some examples include tetracyclines, chloramphenicol, aminoglycosides and macrolides.
Cell Membrane Inhibitors:
Antibiotics such as polymyxins disrupt the integrity and structure of cell membranes, thereby killing them. These set of antibiotics are mostly effective on gram negative bacteria because these are the bacteria that contain a definite cell membrane.
Effect on Nucleic Acids:
DNA and RNA are extremely essential nucleic acids present in every living cell. Antibiotics such as quinolones and rifamycins bind to the proteins that are required for the processing of DNA and RNA, thus blocking their synthesis and thereby affecting the growth of the cells.
Also referred to as anti-metabolites or growth factor analogs, these are antibiotics that competitively inhibit the important metabolic pathways occurring inside the bacterial cell. Important ones in this class are sulfonamides such as Gantrisin and Trimethoprim.