Who discovered the first anti-biotic and what was it?

The first antibacterial substance that can be considered
as a limited-spectrum antibiotic was Salvarsan and it was
discovered in 1910, by the German physician and chemist Paul Ehrlich (1854-1915).
Salvarsan was a medicine meant to cure syphilis, which was very prevalent at that
time.

Salvarsan was followed, in 1928, by the epochal
discovery of Penicillin, by Alexander
Fleming, who noted that secretion of green mold "Penicillium notatum
(Penicillium chrysogenum) destroys bacteria colony from the
laboratory.

Another finding which is worth mentioning is
the discovery in 1935 of sulphonamides, by Gerhard Domagk, who is not an antibiotic,
being not bactericidal but only bacteriostatic.  It follows the discovery of a series of
antibiotics as streptomycin, tetracycline, etc.