Which antibiotic was first time demonstrated by Fleming (1929)

Penicillin antibiotic was first time demonstrated by Fleming (1929).
Scottish physician Alexander Fleming was the first to experimentally discover that a Penicillium mould secretes an antibacterial substance and the first to concentrate the active substance involved, which he named penicillin.
He concluded that the mould was releasing a substance that was inhibiting bacterial growth, and he produced culture broth of the mould and subsequently concentrated the antibacterial component. After testing against different bacteria, he found that the mould could kill only specific bacteria.