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Literally antibiotics are chemical substances extracted from a mould or bacterium that can kill or inhibit the growth of microorganisms.

Antibiotics - substances from one microorganism that can kill or inhibit the growth of another microorganism.

Semisynthetic antibiotics - antibiotic substances derived from a substance produced by a microorganism. 

First antibiotic

Penicillin(derived from the mould Penicillium notatum).

Discovered by: Sir Alexander Fleming in 1928.

Drug mechanism

Antibiotics destroy the cell wall, inhibits protein and nucleic acid synthesis and synthesis of other essential metabolites. Antibiotics, such as penicillin and its derivatives, prevent the synthesis of bacterial cell wall called peptidoglycan.

Since gram-positive cells are composed of more peptidoglycan, these antibiotics are most effective against gram-positive bacteria.


Narrow spectrum antibiotics:

Antibiotics capable of working on limited types of bacteria, such as penicillin are called narrow spectrum antibiotics.

Wide spectrum antibiotics:

Antibiotics that work on many types of bacteria by preventing cell wall synthesis, without affecting the host cells are called wide spectrum antibiotics. These include cephalosporins, bacitracin, isoniazid, and vancomycin.

Inhibitors of protein synthesis:

Antibiotics that work on many types of bacteria by interfering with ribosome function such as chloramphenicol, erythromycin, tetracycline, streptomycin, and gentamicin.

Inhibitors of nucleic acid synthesis:

Antibiotics that inhibit nucleic acid synthesis either interfere with DNA replication or transcription, may also harm the host. Some of the DNA replication inhibiting antibiotics include Rifampin, quinolones, nalidixic acid, nofloxacin, and ciprofloxacin.

Competitive inhibitor antibiotics such as Sulfanilamide, a sulfa drug, mimics the structure of Para Amino Benzoic Acid(PABA) and competes to bind with the enzyme that normally binds PABA, inhibiting the synthesis of folic acid.

Humans are not affected, since, humans obtain folic acid through diet rather than synthesizing it.

Important antibiotics
Bacitracin Effective against several types of Gram-positive organisms.
Cephalosporins Broad spectrum antibiotics.
Chloramphenicol Used against serious infections such as typhoid fever.
Ciprofloxacin Used against anthrax infections.(Trade name: Cipro)
Erythromycin Used to treat infections caused by gram positive bacteria.
Gentamicin Used to treat urinary tract infections.
Isoniazid Used to treat tuberculosis
Penicillin Used in the treatment of various infections.
Quinolones Used against gram negative organisms
Rifampin Used to treat tuberculosis.
Streptomycin Used to treat Tuberculosis
Sulfa drugs Used to inhibit the growth of bacteria that require PABA.
Tetracycline Used to treat infections.
Vancomycin Used against resistant strains of streptococcus and staphylococcus.