Antibiotics are mostly obtained from

The role of bacteria in the carbon cycle is:

$S$ (Assertion): Alexander Fleming established the full potential of penicillin as an effective antibiotic.
$R$ (Reason): Alexander Fleming discovered penicillin.

Who discovered penicillin?

Consider the following statements:
$I.$ Antibiotics are chemical substances produced by some microorganisms which can kill or retard the growth of other disease-causing microorganisms.
$II.$ Penicillin is the first antibiotic discovered by Alexander Fleming $(1928)$,while working on the bacterium $Staphylococcus$ $aureus$.
$III.$ The function of penicillin as an antibiotic was established by Ernst Chain and Howard Florey.
Which of the statements given above are correct?

Alexander Fleming worked on which of the following bacteria?