(a) Antibiotics are the substances produced by micro-organisms which in low concentration are antagonistic to the growth of other microrganisms.
(b) Medicinally antibiotics are those organic secretions which destroy or check the growth of different pathogens without harming the host.
© The first commercial antibiotic was discovered by Flemming (1929) from a fungus called Penicillium.
(d) Maximum number of antibiotics are produced by mycelial bacteria known as actinomycetes. Some important antibiotics are:
(i) Streptomycin - Streptomyces griseus.
(ii) Terramycin - Streptomyces ramosus.
(iii)Chloromycetin - Streptomyces venezuelae.
(iv) Novobiocin - Streptomyces spheroids